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PAX Manual

Table of Contents

[in package MGL-PAX with nicknames PAX]



  • Description: MGL-PAX with all features preloaded.
  • Licence: MIT, see COPYING.
  • Author: Gábor Melis
  • Mailto:

3 Links

Here is the official repository and the HTML documentation for the latest version.

4 Background

As a user, I frequently run into documentation that's incomplete and out of date, so I tend to stay in the editor and explore the code by jumping around with SLIME's M-.. As a library author, I spend a great deal of time polishing code but precious little writing documentation.

In fact, I rarely write anything more comprehensive than docstrings for exported stuff. Writing docstrings feels easier than writing a separate user manual, and they are always close at hand during development. The drawback of this style is that users of the library have to piece the big picture together themselves.

That's easy to solve, I thought, let's just put all the narrative that holds docstrings together in the code and be a bit like a Literate Programmer turned inside out. The original prototype, which did almost everything I wanted, was this:

(defmacro defsection (name docstring)
  `(defun ,name () ,docstring))

Armed with this DEFSECTION, I soon found myself organizing code following the flow of user-level documentation and relegated comments to implementation details entirely. However, some parts of DEFSECTION docstrings were just listings of all the functions, macros and variables related to the narrative, and this list was repeated in the DEFPACKAGE form complete with little comments that were like section names. A clear violation of OAOO, one of them had to go, so DEFSECTION got a list of symbols to export.

That was great, but soon I found that the listing of symbols is ambiguous if, for example, a function, a compiler macro and a class are named by the same symbol. This did not concern exporting, of course, but it didn't help readability. Distractingly, on such symbols, M-. was popping up selection dialogs. There were two birds to kill, and the symbol got accompanied by a type, which was later generalized into the concept of locatives:

(defsection @introduction ()
  "A single line for one man ..."
  (foo class)
  (bar function))

After a bit of elisp hacking, M-. was smart enough to disambiguate based on the locative found in the vicinity of the symbol, and everything was good for a while.

Then I realized that sections could refer to other sections if there were a SECTION locative. Going down that path, I soon began to feel the urge to generate pretty documentation as all the necessary information was manifest in the DEFSECTION forms. The design constraint imposed on documentation generation was that following the typical style of upcasing symbols in docstrings there should be no need to explicitly mark up links: if M-. works, then the documentation generator shall also be able find out what's being referred to.

I settled on Markdown as a reasonably non-intrusive format, and a few thousand lines later PAX was born.

5 Tutorial

PAX provides an extremely poor man's Explorable Programming environment. Narrative primarily lives in so called sections that mix markdown docstrings with references to functions, variables, etc, all of which should probably have their own docstrings.

The primary focus is on making code easily explorable by using SLIME's M-. (slime-edit-definition). See how to enable some fanciness in Navigating Sources in Emacs. Generating Documentation from sections and all the referenced items in Markdown or HTML format is also implemented.

With the simplistic tools provided, one may accomplish similar effects as with Literate Programming, but documentation is generated from code, not vice versa and there is no support for chunking. Code is first, code must look pretty, documentation is code.


PAX's automatically recognizes and marks up code with backticks and links code to their definitions.

(document "&KEY arguments such as :IF-EXISTS are common.")
=> ("`&KEY` arguments such as `:IF-EXISTS` are common.

(document "AND denotes a macro and a type specifier.
          Here we focus on the macro AND.")
=> ("`AND`([`0`][4954] [`1`][330f]) denotes a macro and a type specifier.
Here we focus on the macro [`AND`][4954].

  [330f]: \"AND TYPE\"
  [4954]: \"AND MGL-PAX:MACRO\"

These features are designed to handle a common style of docstrings with minimal additional markup. The following is the output of (mgl-pax:document #'abort). Note that the docstring of the ABORT function was not written with PAX in mind.


    Transfer control to a restart named ABORT, signalling a CONTROL-ERROR if none exists.

A Complete Example

Here is an example of how it all works together:

(mgl-pax:define-package :foo-random
  (:documentation "This package provides various utilities for random.
  (:use #:common-lisp #:mgl-pax))

(in-package :foo-random)

(defsection @foo-random-manual (:title "Foo Random manual")
  "Here you describe what's common to all the referenced (and
  exported) functions that follow. They work with *FOO-STATE*, and
  have a :RANDOM-STATE keyword arg. Also explain when to choose
  (foo-random-state class)
  (state (reader foo-random-state))
  "Hey we can also print states!"
  (print-object (method () (foo-random-state t)))
  (*foo-state* variable)
  (gaussian-random function)
  (uniform-random function)
  ;; This is a subsection.
  (@foo-random-examples section))

(defclass foo-random-state ()
  ((state :reader state)))

(defmethod print-object ((object foo-random-state) stream)
  (print-unreadable-object (object stream :type t)))

(defvar *foo-state* (make-instance 'foo-random-state)
  "Much like *RANDOM-STATE* but uses the FOO algorithm.")

(defun uniform-random (limit &key (random-state *foo-state*))
  "Return a random number from the between 0 and LIMIT (exclusive)
  uniform distribution."

(defun gaussian-random (stddev &key (random-state *foo-state*))
  "Return a random number from a zero mean normal distribution with

(defsection @foo-random-examples (:title "Examples")
  "Let's see the transcript of a real session of someone working
  with FOO:

  (values (princ :hello) (list 1 2))
  .. HELLO
  => :HELLO
  => (1 2)

  (make-instance 'foo-random-state)

Note how (VARIABLE *FOO-STATE*) in the DEFSECTION form both exports *FOO-STATE* and includes its documentation in @FOO-RANDOM-MANUAL. The symbols VARIABLE and FUNCTION are just two instances of locatives, which are used in DEFSECTION to refer to definitions tied to symbols.

(DOCUMENT @FOO-RANDOM-MANUAL) generates fancy markdown or HTML output with automatic markup and autolinks uppercase words found in docstrings, numbers sections, and creates a table of contents.

One can even generate documentation for different but related libraries at the same time with the output going to different files but with cross-page links being automatically added for symbols mentioned in docstrings. See Generating Documentation for some convenience functions to cover the most common cases.

The transcript in the code block tagged with cl-transcript is automatically checked for up-to-dateness when documentation is generated.

6 Basics

Now let's examine the most important pieces.


    Define a documentation section and maybe export referenced symbols. A bit behind the scenes, a global variable with NAME is defined and is bound to a SECTION object. By convention, section names start with the character @. See Tutorial for an example.


    ENTRIES consists of docstrings and references in any order. Docstrings are arbitrary strings in markdown format.

    REFERENCES are given in the form (OBJECT LOCATIVE). For example, (FOO FUNCTION) refers to the function FOO, (@BAR SECTION) says that @BAR is a subsection of this one. (BAZ (METHOD () (T T T))) refers to the default method of the three argument generic function BAZ. (FOO FUNCTION) is equivalent to (FOO (FUNCTION)). See Locatives and References for more.

    The same object may occur in multiple references, typically with different locatives, but this is not required.

    The references are not looked up (see RESOLVE in the Locatives and References API) until documentation is generated, so it is allowed to refer to things yet to be defined.


    If EXPORT is true (the default), NAME and the objects of references among ENTRIES which are SYMBOLs are candidates for exporting. A candidate symbol is exported if

    See DEFINE-PACKAGE if you use the export feature. The idea with confounding documentation and exporting is to force documentation of all exported symbols.


    TITLE is a string containing markdown or NIL. If non-NIL, it determines the text of the heading in the generated output. LINK-TITLE-TO is a reference given as an (OBJECT LOCATIVE) pair or NIL, to which the heading will link when generating HTML. If not specified, the heading will link to its own anchor.

    When DISCARD-DOCUMENTATION-P (defaults to *DISCARD-DOCUMENTATION-P*) is true, ENTRIES will not be recorded to save memory.


    The default value of DEFSECTION's DISCARD-DOCUMENTATION-P argument. One may want to set *DISCARD-DOCUMENTATION-P* to true before building a binary application.


    This is like CL:DEFPACKAGE but silences warnings and errors signaled when the redefined package is at variance with the current state of the package. Typically this situation occurs when symbols are exported by calling EXPORT (as is the case with DEFSECTION) as opposed to adding :EXPORT forms to the DEFPACKAGE form and the package definition is subsequently reevaluated. See the section on package variance in the SBCL manual.

    The bottom line is that if you rely on DEFSECTION to do the exporting, then you'd better use DEFINE-PACKAGE.

6.1 Locatives and References

To navigate with M-. and to generate documentation we need to refer to things such as the FOO type or the FOO function.

(deftype foo ()
  "type doc"
  '(or integer real).

(defun foo ()
  "function doc"

The docstring is available via (CL:DOCUMENTATION 'FOO 'TYPE), where TYPE - called DOC-TYPE - is what tells CL:DOCUMENTATION that we want the docstring of the type named FOO. This design supports disambiguation and working with things that are not first-class, such as types.

PAX generalizes DOC-TYPE to the concept of locatives, which may also take arguments. An object and a locative together are called a reference, and they identify a definition. REFERENCEs are actual objects, but often they appear as an (OBJECT LOCATIVE) list (see DEFSECTION) or as "OBJECT LOCATIVE" in docstrings (see Linking to Code for the various forms possible).

(defsection @foos ()
  "We discuss the FOO type and the FOO function."
  (foo type)
  (foo function))

  • [glossary-term] reference

    A reference is an object plus a locative, and it identifies a definition. For example, the symbol FOO as the object and the symbol FUNCTION as the locative together refer to the global definition of the function FOO.

    REFERENCE objects can be represented as an (OBJECT LOCATIVE) list as in DEFSECTION entries, or textually as "FOO function" where FOO is a name or similar (see Codification and Linking to Code).

  • [glossary-term] locative

    locatives specify a type of definition such as FUNCTION or VARIABLE and together with objects form references.

    A locative can be a symbol or a list whose CAR is a symbol. In either case, the symbol is called the locative type while the rest of the elements are the locative arguments. See the METHOD locative or the LOCATIVE locative for examples of locative types with arguments.

6.1.1 Locatives and References API

(MAKE-REFERENCE 'FOO 'VARIABLE) constructs a REFERENCE that captures the path to take from an object (the symbol FOO) to an entity of interest (for example, the documentation of the variable). The path is called the locative. A locative can be applied to an object like this:

(locate 'foo 'variable)

which will return the same reference as (MAKE-REFERENCE 'FOO 'VARIABLE). Operations need to know how to deal with references, which we will see in the Writing Extensions.

Naturally, (LOCATE 'FOO 'FUNCTION) will simply return #'FOO, no need to muck with references when there is a perfectly good object.





    Return the first element of LOCATIVE if it's a list. If it's a symbol, then return that symbol itself.


    The REST of LOCATIVE if it's a list. If it's a symbol then it's NIL.


    Follow LOCATIVE from OBJECT and return the object it leads to or a REFERENCE if there is no first-class object corresponding to the location. Depending on ERRORP, a LOCATE-ERROR condition is signaled or NIL is returned if the lookup fails.

    (locate 'locate 'function)
    (locate 'no-such-function 'function)
    .. debugger invoked on LOCATE-ERROR:
    ..   Could not locate NO-SUCH-FUNCTION FUNCTION.
    ..   NO-SUCH-FUNCTION does not name a function.
    (locate 'locate-object 'method)
    .. debugger invoked on LOCATE-ERROR:
    ..   Could not locate LOCATE-OBJECT METHOD.
    ..   The syntax of the METHOD locative is (METHOD <METHOD-QUALIFIERS> <METHOD-SPECIALIZERS>).

  • [condition] LOCATE-ERROR ERROR

    Signaled by LOCATE when the lookup fails and ERRORP is true.





    A convenience function to LOCATE REFERENCE's object with its locative.

6.2 Parsing

  • [glossary-term] word

    A word is a string from which we want to extract an object. When Navigating, the word is slime-symbol-at-point. When Generating Documentation, it is a non-empty string between whitespace characters in a docstring.

  • [glossary-term] name

    A name is a string that names an INTERNed SYMBOL, a PACKAGE(0 1), or an ASDF:SYSTEM, that is, a possible object. Names are constructed from words by possibly trimming leading and trailing punctuation symbols and removing certain plural suffixes.

    For example, in "X and Y must be LISTs.", although the word is "LISTs.", it gets trimmed to "LISTs", then the plural suffix "s" is removed to get "LIST". Out of the three candidates for names, "LISTs.", "LISTs", and "LIST", the ones that name interned symbols and such are retained for purposes for Navigating and Generating Documentation.

    The punctuation characters for left and right trimming are #< and ,:.>, respectively. The plural suffixes considered are s, es, ses, zes, and ren (all case insensitive).

    Thus "CHILDREN" and "BUSES" may have the names "CHILD" and "BUS" in them.

7 Locative Types

As we have already briefly seen in DEFSECTION and Locatives and References, locatives allow us to refer to, document, and find the source location of various definitions beyond what standard Common Lisp offers. See Writing Extensions for a more detailed treatment. The following are the locatives types supported out of the box. As all locative types, they are named by symbols, which should make it obvious what kind of things they refer to. Unless otherwise noted, locatives take no arguments.

When there is a corresponding CL type, a locative can be resolved to a unique object as is the case in (LOCATE 'FOO 'CLASS) returning #<CLASS FOO>. Even if there is no such CL type, the source location and the docstring of the defining form is recorded (see LOCATE-AND-FIND-SOURCE, LOCATE-AND-DOCUMENT in the Writing Extensions), which makes navigating the sources with M-. (see Navigating Sources in Emacs) and Generating Documentation possible.

7.1 Locatives for Variables


    Refers to a global special variable. INITFORM, or if not specified, the global value of the variable is included in the documentation.

    ;;; A REFERENCE is returned because there is no such type as VARIABLE.
    (locate '*FORMAT* 'variable)

    For the output of (DOCUMENT (MAKE-REFERENCE '*FORMAT* 'VARIABLE)), see *FORMAT*. Note that *FORMAT* is unbound. If the variable is BOUNDP, then its current value is included in the documentation. See *DOCUMENT-LINK-CODE* for an example output. To override the current value, INITFORM may be provided. This is particulary useful if the value of the variable is something undesirable such as #<MY-CLASS {100171ED93}>.


    Refers to a variable defined with DEFCONSTANT. INITFORM, or if not specified, the value of the constant is included in the documentation. The CONSTANT locative is like the VARIABLE locative, but it also checks that its object is CONSTANTP.

7.2 Locatives for Macros

  • [locative] SYMBOL-MACRO

    Refers to a global symbol macro, defined with DEFINE-SYMBOL-MACRO. Note that since DEFINE-SYMBOL-MACRO does not support docstrings, PAX defines methods on the DOCUMENTATION generic function specialized for DOC-TYPE SYMBOL-MACRO.

    (define-symbol-macro my-mac 42)
    (setf (documentation 'my-mac 'symbol-macro)
          "This is MY-MAC.")
    (documentation 'my-mac 'symbol-macro)
    => "This is MY-MAC."

  • [locative] COMPILER-MACRO

    Refers to a compiler macro, typically defined with DEFINE-COMPILER-MACRO. See the FUNCTION locative for a note on arglists.

7.3 Locatives for Functions

  • [locative] FUNCTION

    Refers to a global function, typically defined with DEFUN.

    Note that the arglist in the generated documentation depends on the quality of SWANK-BACKEND:ARGLIST. It may be that default values of optional and keyword arguments are missing.


    See CL:FIND-METHOD for the description of the arguments METHOD-QUALIFIERS and METHOD-SPECIALIZERS. For example, a (FOO (METHOD () (T (EQL XXX)))) as a DEFSECTION entry refers to this method:

      (defmethod foo (x (y (eql 'xxx)))


  • [locative] ACCESSOR CLASS-NAME

    To refer to an accessor named FOO-SLOT of class FOO:

      (foo-slot (accessor foo))

  • [locative] READER CLASS-NAME

    To refer to a reader named FOO-SLOT of class FOO:

      (foo-slot (reader foo))

  • [locative] WRITER CLASS-NAME

    To refer to a writer named FOO-SLOT of class FOO:

      (foo-slot (writer foo))


    This is a synonym of FUNCTION with the difference that the often ugly and certainly uninformative lambda list will not be printed.

7.4 Locatives for Types and Declarations

  • [locative] TYPE

    This locative can refer to any Lisp type. For types defined with DEFTYPE, an attempt is made at printing the arguments of type specifiers. When TYPE refers to a CL:CLASS, the class is documented as an opaque type: no mention is made of that it is a class or its superclasses. Use the CLASS locative if those things are part of the contract.

  • [locative] CLASS

    Naturally, CLASS is the locative type for CLASSes. To refer to a class named FOO:

      (foo class)

    In the generated documention, only superclasses denoted by external symbols are included.

  • [locative] DECLARATION

    Refers to a declaration, used in DECLARE, DECLAIM and PROCLAIM. For example, [DEBUG][declaration] refers to the standard DEBUG declaration and links to the hyperspec if *DOCUMENT-LINK-TO-HYPERSPEC* is true.

    User code may also define new declarations with CLTL2 functionality, but there is no way to provide a docstring.

    (cl-environments:define-declaration my-decl (&rest things)
      (values :declare (cons 'foo things)))

    Also, M-. (see Navigating Sources in Emacs) on declarations currently only works on SBCL.

7.5 Condition System Locatives

  • [locative] CONDITION

    CONDITION is the locative type for CONDITIONs. To refer to a condition named FOO:

      (foo condition)

    In the generated documention, only superclasses denoted by external symbols are included.

  • [locative] RESTART

    A locative to refer to the definition of a restart defined by DEFINE-RESTART.


    A definer macro to hang the documentation of a restart on a symbol.

    (define-restart my-ignore-error ()
      "Available when MY-ERROR is signalled, MY-IGNORE-ERROR unsafely continues.")

    Then (MY-IGNORE-ERROR RESTART) refers to the above definition. Note that while there is a CL:RESTART type, there is no corresponding source location or docstring like for CONDITIONs.

7.6 Locatives for Packages and Readtables

  • [locative] ASDF/SYSTEM:SYSTEM

    Refers to an asdf system. The generated documentation will include meta information extracted from the system definition. This also serves as an example of a symbol that's not accessible in the current package and consequently is not exported.


  • [locative] READTABLE

    Refers to a named READTABLE defined with NAMED-READTABLES:DEFREADTABLE, which associates a global name and a docstring with the readtable object. Unfortunately, source location information is not available.

7.7 Locatives for PAX Constructs


    Define a global variable with NAME and set it to a GLOSSARY-TERM object. A glossary term is just a symbol to hang a docstring on. It is a bit like a SECTION(0 1) in that, when linked to, its TITLE will be the link text instead of the name of the symbol. Also as with sections, both TITLE and DOCSTRING are markdown strings or NIL.

    Unlike sections though, glossary terms are not rendered with headings, but in the more lightweight bullet + locative + name/title style. See the glossary entry name for an example.

    When DISCARD-DOCUMENTATION-P (defaults to *DISCARD-DOCUMENTATION-P*) is true, DOCSTRING will not be recorded to save memory.



    This is the locative for locatives. When M-. is pressed on SOME-NAME in (SOME-NAME LOCATIVE), this is what makes it possible to land at the corresponding DEFINE-LOCATIVE-TYPE form. Similarly, (LOCATIVE LOCATIVE) leads to this very definition.

  • [locative] DISLOCATED

    Refers to a symbol in a non-specific context. Useful for preventing autolinking. For example, if there is a function called FOO then


    will be linked (if *DOCUMENT-LINK-CODE*) to its definition. However,


    will not be. With a dislocated locative, LOCATE always fails with a LOCATE-ERROR condition. Also see Preventing Autolinking.

  • [locative] ARGUMENT

    An alias for DISLOCATED, so that one can refer to an argument of a macro without accidentally linking to a class that has the same name as that argument. In the following example, FORMAT may link to CL:FORMAT (if we generated documentation for it):


    Since ARGUMENT is a locative, we can prevent that linking by writing:

    "See the FORMAT argument of DOCUMENT."


    This pseudolocative refers to a region of a file. SOURCE can be a STRING or a PATHNAME in which case the whole file is being pointed to, or it can explicitly supply START, END locatives. INCLUDE is typically used to include non-lisp files in the documentation (say markdown or elisp as in the next example) or regions of lisp source files. This can reduce clutter and duplication.

    (defsection example-section ()
      (pax.el (include #.(asdf:system-relative-pathname :mgl-pax "src/pax.el")
                       :header-nl "```elisp" :footer-nl "```"))
      (foo-example (include (:start (foo function)
                             :end (end-of-foo-example variable))
                            :header-nl "```"
                            :footer-nl "```"))
    (defun foo (x)
      (1+ x))
    ;;; Since file regions are copied verbatim, comments survive.
    (defmacro bar ())
    ;;; This comment is the last thing in FOO-EXAMPLE's
    ;;; documentation since we use the dummy END-OF-FOO-EXAMPLE
    ;;; variable to mark the end location.
    (defvar end-of-foo-example)
    ;;; More irrelevant code follows.

    In the above example, pressing M-. on PAX.EL will open the src/pax.el file and put the cursor on its first character. M-. on FOO-EXAMPLE will go to the source location of the (asdf:system locative) locative.

    When documentation is generated, the entire src/pax.el file is included in the markdown surrounded by the strings given as HEADER-NL and FOOTER-NL (if any). The trailing newline character is assumed implicitly. If that's undesirable, then use HEADER and FOOTER instead. The documentation of FOO-EXAMPLE will be the region of the file from the source location of the START locative (inclusive) to the source location of the END locative (exclusive). START and END default to the beginning and end of the file, respectively.

    Note that the file of the source location of :START and :END must be the same. If SOURCE is a pathname designator, then it must be absolute so that the locative is context independent.

    Finally, if specified, LINE-PREFIX is a string that's prepended to each line included in the documentation. For example, a string of four spaces makes markdown think it's a code block.


  • [locative] DOCSTRING

    DOCSTRING is a pseudolocative for including the parse tree of the markdown DOCSTRING of a definition in the parse tree of a docstring when generating documentation. It has no source location information and only works as an explicit link. This construct is intended to allow docstrings live closer to their implementation, which typically involves a non-exported definition.

    (defun div2 (x)
      "X must be an [even type][docstring]."
      (/ x 2))
    (deftype even ()
      "an even integer"
      '(satisfies oddp))

    In the output of (DOCUMENT #'DIV2), we have that X must be an an even integer.

7.8 External Locatives

  • [locative] CLHS

    Refers to sections in the Common Lisp hyperspec. These have no source location so M-. will not work. What works is linking. The following markdown examples all produce a link to CLHS 3.4, the section 'Lambda Lists', which is in file 03_d.htm.

    CLHS `3.4`
    `3.4` CLHS
    [Lambda Lists][clhs]

    The rules of matching sections are the following. If the object of the reference is STRING= to the section number string (without the trailing dot) or to the name of its file without the .htm extension, then the reference refers to that section. Else, if the object is a case-insensitive substring of the title of some section, then the reference refers to the first such section in breadth-first order.

    To link to issue and issue summary pages, all of the above markdown examples work, just make the object of the reference the name of the issue prefixed by ISSUE: or SUMMARY: as appropriate. For example, to refer to the AREF-1D issue use [ISSUE:AREF-1D][clhs] and get ISSUE:AREF-1D. Similary, [SUMMARY:AREF-1D][clhs] turns into SUMMARY:AREF-1D. Alternatively, matching the name of the file also works ([iss009][clhs] renders as iss009)

    The generated links are relative to *DOCUMENT-HYPERSPEC-ROOT*.

    To detach the discussion from markdown syntax, let's see these cases through the programmatic interface.

    (locate "3.4" 'clhs)
    ==> #<REFERENCE "3.4" CLHS>
    (locate "03_d" 'clhs)
    ==> #<REFERENCE "03_d" CLHS>
    (locate "lambda" 'clhs)
    ==> #<REFERENCE "3.4" CLHS>
    (locate "ISSUE:AREF-1D" 'clhs)
    (locate "SUMMARY:AREF-1D" 'clhs)

8 Navigating Sources in Emacs

Integration into SLIME's M-. (slime-edit-definition) allows one to visit the source location of the definition that's identified by slime-symbol-at-point parsed as a word and the locative before or after the symbol in a buffer. With this extension, if a locative is the previous or the next expression around the symbol of interest, then M-. will go straight to the definition which corresponds to the locative. If that fails, M-. will try to find the definitions in the normal way, which may involve popping up an xref buffer and letting the user interactively select one of possible definitions.

In the following examples, when the cursor is on one of the characters of FOO or just after FOO, pressing M-. will visit the definition of function FOO:

function foo
foo function
(function foo)
(foo function)

In particular, references in a DEFSECTION form are in (SYMBOL LOCATIVE) format so M-. will work just fine there.

Just like vanilla M-., this works in comments and docstrings. In the next example, pressing M-. on FOO will visit FOO's default method:

;;;; See FOO `(method () (t t t))` for how this all works.
;;;; But if the locative has semicolons inside: FOO `(method
;;;; () (t t t))`, then it won't, so be wary of line breaks
;;;; in comments.

With a prefix argument (C-u M-.), one can enter a symbol plus a locative separated by whitespace to preselect one of the possibilities.

The M-. extensions can be enabled by loading src/pax.el.


9 Generating Documentation


    Write OBJECT in FORMAT to STREAM diverting some output to PAGES. FORMAT can be anything 3BMD supports, which is currently :MARKDOWN, :HTML and :PLAIN. STREAM may be a STREAM object, T or NIL as with CL:FORMAT.

    Most often, this function is called on SECTION(0 1) objects as in (DOCUMENT @PAX-MANUAL), but it supports all kinds of objects for which DOCUMENT-OBJECT is defined. To look up the documentation of the DOCUMENT function itself:

      (document #'document)

    The same with fancy markup:

      (document #'document :format :markdown)

    To generate the documentation for separate libraries with automatic cross-links:

      (document (list @cube-manual @mat-manual) :format :markdown)

    See Utilities for Generating Documentation for more.

    Note that not only first-class objects can have documentation:

      (document (locate 'foo 'type))

    See Locatives and References for more.

    There are quite a few special variables that affect how output is generated, see Codification, Linking to Code, Linking to Sections, and Miscellaneous Variables.

    If PAGES is NIL and STREAM is NIL, then DOCUMENT returns the output as a string. If PAGES is NIL but STREAM is not, then DOCUMENT returns NIL. The rest of this description deals with how to generate multiple pages.


    The PAGES argument is to create multi-page documents by routing some of the generated output to files, strings or streams. PAGES is a list of page specification elements. A page spec is a plist with keys :OBJECTS, :OUTPUT, :URI-FRAGMENT, :SOURCE-URI-FN, :HEADER-FN and :FOOTER-FN. OBJECTS is a list of objects (references are allowed but not required) whose documentation is to be sent to :OUTPUT.

    When documentation for an object is generated, the first matching page spec is used, where the object matches the page spec if it is reachable from one of its :OBJECTS.

    :OUTPUT can be a number things:

    • If it's a list whose first element is a string or a pathname, then output will be sent to the file denoted by that and the rest of the elements of the list are passed on to CL:OPEN. One extra keyword argument is :ENSURE-DIRECTORIES-EXIST. If it's true, ENSURE-DIRECTORIES-EXIST will be called on the pathname before it's opened.

    • If it's NIL, then output will be collected in a string.

    • If it's T, then output will be sent to *STANDARD-OUTPUT*.

    • If it's a stream, then output will be sent to that stream.

    If some pages are specified, DOCUMENT returns a list of designators for generated output. If a page whose :OUTPUT refers to a file that was created (which doesn't happen if nothing would be written to it), then the corresponding pathname is included in the list. For strings the string itself, while for streams the stream object is included in the list. This way it's possible to write some pages to files and some to strings and have the return value indicate what was created. The output designators in the returned list are ordered by creation time.

    Note that even if PAGES is specified, STREAM acts as a catch all, taking the generated documentation for references not claimed by any pages. Also, the filename, string or stream corresponding to STREAM is always the first element in the list of generated things, that is the return value.

    :HEADER-FN, if not NIL, is a function of a single stream argument, which is called just before the first write to the page. Since :FORMAT :HTML only generates HTML fragments, this makes it possible to print arbitrary headers, typically setting the title, css stylesheet, or charset.

    :FOOTER-FN is similar to :HEADER-FN, but it's called after the last write to the page. For HTML, it typically just closes the body.

    :URI-FRAGMENT is a string such as "doc/manual.html" that specifies where the page will be deployed on a webserver. It defines how links between pages will look. If it's not specified and :OUTPUT refers to a file, then it defaults to the name of the file. If :URI-FRAGMENT is NIL, then no links will be made to or from that page.

    Finally, :SOURCE-URI-FN is a function of a single, REFERENCE argument. If it returns a value other than NIL, then it must be a string representing an URI. If FORMAT is :HTML and *DOCUMENT-MARK-UP-SIGNATURES* is true, then the locative as displayed in the signature will be a link to this uri. See MAKE-GIT-SOURCE-URI-FN.

    PAGES may look something like this:

    `((;; The section about SECTIONs and everything below it ...
       :objects (, @sections)
       ;; ... is so boring that it's not worth the disk space, so
       ;; send it to a string.
       :output (nil)
       ;; Explicitly tell other pages not to link to these guys.
       :uri-fragment nil)
      ;; Send the @EXTENSION-API section and everything reachable
      ;; from it ...
      (:objects (, @extension-api)
       ;; ... to build/tmp/pax-extension-api.html.
       :output ("build/tmp/pax-extension-api.html")
       ;; However, on the web server html files will be at this
       ;; location relative to some common root, so override the
       ;; default:
       :uri-fragment "doc/dev/pax-extension-api.html"
       ;; Set html page title, stylesheet, charset.
       :header-fn 'write-html-header
       ;; Just close the body.
       :footer-fn 'write-html-footer)
      ;; Catch the reference that were not reachable from the above. It
      ;; is important for this page spec to be last.
      (:objects (, @pax-manual)
       :output ("build/tmp/manual.html")
       ;; Links from the extension api page to the manual page will
       ;; be to ../user/pax-manual#<anchor>, while links going to
       ;; the opposite direction will be to
       ;; ../dev/pax-extension-api.html#<anchor>.
       :uri-fragment "doc/user/pax-manual.html"
       :header-fn 'write-html-header
       :footer-fn 'write-html-footer))


9.2 Markdown Support

The Markdown in docstrings is processed with the 3BMD library.

9.2.1 Indentation

Docstrings can be indented in any of the usual styles. PAX normalizes indentation by converting:

(defun foo ()
  "This is


(defun foo ()
  "This is

See DOCUMENT-OBJECT for the details.


    Print STRING to STREAM as a docstring. That is, clean up indentation, perform Codification, and linking (see Linking to Code, Linking to the Hyperspec).

    Docstrings in sources are indented in various ways, which can easily mess up markdown. To handle the most common cases leave the first line alone, but from the rest of the lines strip the longest run of leading spaces that is common to all non-blank lines.

9.2.2 Syntax Highlighting

For syntax highlighting, github's fenced code blocks markdown extension to mark up code blocks with triple backticks is enabled so all you need to do is write:

(defun foo ())

to get syntactically marked up HTML output. Copy src/style.css from PAX and you are set. The language tag, elisp in this example, is optional and defaults to common-lisp.

See the documentation of 3BMD and colorize for the details.

9.2.3 MathJax

Displaying pretty mathematics in TeX format is supported via MathJax. It can be done inline with $ like this:

$\int_0^\infty e^{-x^2} dx=\frac{\sqrt{\pi}}{2}$

which is diplayed as $\int_0^\infty e^{-x^2} dx=\frac{\sqrt{\pi}}{2}$, or it can be delimited by $$ like this:

$$\int_0^\infty e^{-x^2} dx=\frac{\sqrt{\pi}}{2}$$

to get: $$\int_0^\infty e^{-x^2} dx=\frac{\sqrt{\pi}}{2}$$

MathJax will leave code blocks (including those inline with backticks) alone. Outside code blocks, escape $ by prefixing it with a backslash to scare MathJax off.

Escaping all those backslashes in TeX fragments embedded in Lisp strings can be a pain. Pythonic String Reader can help with that.

9.3 Codification


    When true, codifiable and interesting words are assumed to be code as if they were marked up with backticks. For example, this docstring

      CaMeL Capital"

    is equivalent to this:

      CaMel Capital"

    and renders as

    T PRINT CLASS(0 1)es SECTION(0 1) MGL-PAX ASDF CaMel Capital

    where the links are added due to *DOCUMENT-LINK-CODE*.

    To suppress this behavior, add a backslash to the beginning of the a codifiable word or right after the leading * if it would otherwise be parsed as markdown emphasis:

      "\\SECTION *\\PACKAGE*"

    The number of backslashes is doubled above because that's how the example looks in a docstring. Note that the backslash is discarded even if *DOCUMENT-UPPERCASE-IS-CODE* is false.

  • [glossary-term] codifiable

    A word is codifiable iff

    • it has at least one uppercase character (e.g. it's not <, <= or ///), and

    • it has no lowercase characters (e.g. it's T, or *PRINT-LENGTH*) or all lowercase characters immediately follow at least two consecutive uppercase characters (e.g. in CLASSes(0 1) but in not Capital).

  • [glossary-term] interesting

    A word is interesting iff it names

    • a known reference, or

    • a symbol external to its package, or

    • it is at least 3 characters long and names an interned symbol.

    Where we say that a word names a known reference if the word matches the name of a thing being documented, or it is in the hyperspec and *DOCUMENT-LINK-TO-HYPERSPEC* is true. More precisely, a word names a known reference, if it matches

    Symbols are read in the current *PACKAGE*, which is subject to *DOCUMENT-NORMALIZE-PACKAGES*.


    If true, then all Markdown inline code (that is, stuff between backticks, including those found if *DOCUMENT-UPPERCASE-IS-CODE*) which has no lowercase characters is downcased in the output. Characters of literal strings in the code may be of any case. If this variable is :ONLY-IN-MARKUP and the output format does not support markup (e.g. it's :PLAIN), then no downcasing is performed. For example,

      `(PRINT "Hello")`

    is downcased to

      `(print "Hello")`

    because it only contains uppercase characters outside the string. However,

      `MiXed "RESULTS"`

    is not altered because it has lowercase characters.

    If the first two characters are backslashes, then no downcasing is performed, in addition to Preventing Autolinking. Use this to mark inline code that's not Lisp.

      Press `\\M-.` in Emacs.

9.4 Linking to Code

In this section, we describe all ways of linking to code available when *DOCUMENT-UPPERCASE-IS-CODE* is true.

Note that invoking M-. on the object of any of the following links will disambiguate based the textual context, determining the locative. In a nutshell, if M-. works without popping up a list of choices, then the documentation will contain a single link.

  • [variable] *DOCUMENT-LINK-CODE* T

    Enable the various forms of links in docstrings described in Linking to Code. See the following sections for a description of how to use linking.

9.4.1 Specified Locative

The following examples all render as DOCUMENT.

  • [DOCUMENT][function] (object + locative, explicit link)

  • DOCUMENT function (object + locative, autolink)

  • function DOCUMENT (locative + object, autolink)

The Markdown link definition (i.e. function between the second set of brackets above) needs no backticks to mark it as code.

Here and below, the object (DOCUMENT) is uppercased, and we rely on *DOCUMENT-UPPERCASE-IS-CODE* being true. Alternatively, the object could be explicitly marked up as code with a pair of backticks, and then its character case would likely not matter (subject to READTABLE-CASE).

The link text in the above examples is DOCUMENT. To override it, this form may be used:

  • [see this][document function] (title + object + locative, explicit link) renders as: see this.

9.4.2 Unambiguous Unspecified Locative

In the following examples, although no locative is specified, DOCUMENT names a single object being documented, so they all render as DOCUMENT.

  • [DOCUMENT][] (object, explicit link),

  • DOCUMENT (object, autolink).

To override the title:

  • [see this][document] (title + object, explicit link) renders as: see this.

9.4.3 Ambiguous Unspecified Locative

These examples all render as SECTION(0 1), linking to both definitions of the object SECTION, the CLASS and the LOCATIVE.

  • [SECTION][] (object, explicit link)

  • SECTION (object, autolink)

To override the title:

  • [see this][section] (title + object, explicit link) renders as: see this(0 1).

9.4.4 Explicit and Autolinking

The examples in the previous sections are marked with explicit link or autolink. Explicit links are those with a Markdown reference link spelled out explicitly, while autolinks are those without.

9.4.5 Preventing Autolinking

In the common case, when *DOCUMENT-UPPERCASE-IS-CODE* is true, prefixing the uppercase word with a backslash prevents it from being codified and thus also prevents autolinking form kicking in. For example,


renders as DOCUMENT. If it should be marked up as code but not autolinked, the backslash must be within backticks like this:


This renders as DOCUMENT. Alternatively, the DISLOCATED or the ARGUMENT locative may be used as in [DOCUMENT][dislocated].

9.4.6 Unresolvable Links


    When DOCUMENT encounters an explicit link such as [NONEXISTENT][function] that looks like a PAX construct but cannot be resolved, it signals and UNRESOLVABLE-REFLINK warning.

    • If the OUTPUT-REFLINK restart is invoked, then no warning is printed and the markdown link is left unchanged. MUFFLE-WARNING(0 1) is equivalent to OUTPUT-REFLINK.

    • If the OUTPUT-LABEL restart is invoked, then no warning is printed and the markdown link is replaced by its label. For example, [NONEXISTENT][function] becomes NONEXISTENT.

    • If the warning is not handled, then it is printed to *ERROR-OUTPUT*. Otherwise, it behaves as OUTPUT-REFLINK.


    Invoke the OUTPUT-REFLINK restart.


    Invoke the OUTPUT-L restart.

9.4.7 Suppressed Links

Within the same docstring, autolinking of code (i.e. of something like FOO) is suppressed if the same object was already linked to in any way. In the following docstring, only the first FOO will be turned into a link.

"`FOO` is safe. `FOO` is great."

However if a locative was specified or found near the object, then a link is always made. In the following, in both docstrings, both occurrences FOO produce links.

"`FOO` is safe. [`FOO`][macro] is great."
"`FOO` is safe. Macro `FOO` is great."

As an exception, links with specified and unambiguous locatives to SECTION(0 1)s and GLOSSARY-TERM(0 1)s always produce a link to allow their titles to be displayed properly.

Finally, autolinking to T or NIL is suppressed (see *DOCUMENT-LINK-TO-HYPERSPEC*).

9.4.8 Filtering Ambiguous References

When there are multiple references to link to - as seen in Ambiguous Unspecified Locative - some references are removed by the following rules.

  • References to ASDF:SYSTEMs are removed if there are other references which are not to ASDF:SYSTEMs. This is because system names often collide with the name of a class or function and are rarely useful to link to. Use explicit links to ASDF:SYSTEMs, if necessary.

  • References to the CLHS are filtered similarly.

  • If references include a GENERIC-FUNCTION locative, then all references with LOCATIVE-TYPE METHOD, ACCESSOR, READER and WRITER are removed to avoid linking to a possibly large number of methods.

9.4.9 Local References

To unclutter the generated output by reducing the number of links, the so-called 'local' references (e.g. references to the very definition for which documentation is being generated) are treated specially. In the following example, there are local references to the function FOO and its arguments, so none of them get turned into links:

(defun foo (arg1 arg2)
  "FOO takes two arguments: ARG1 and ARG2."

If linking was desired, one could use a Specified Locative (e.g. [FOO][function] or FOO function), which results in a single link. An explicit link with an unspecified locative like [FOO][] generates links to all references involving the FOO symbol except the local ones.

The exact rules for local references are as follows:

  • Unless a locative is specified, no autolinking is performed for objects for which there are local references. For example, FOO does not get any links if there is any local reference with the same object.

  • With a locative specified (e.g. in the explicit link [FOO][function] or in the text the FOO function), a single link is made irrespective of any local references.

  • Explicit links with an unspecified locative (e.g. [FOO][]) are linked to all non-local references.

9.5 Linking to the Hyperspec


    If true, link symbols found in code to the Common Lisp Hyperspec.

    Locatives work as expected (see *DOCUMENT-LINK-CODE*): FIND-IF links to FIND-IF, FUNCTION links to FUNCTION and [FUNCTION][type] links to FUNCTION.

    Autolinking to T and NIL is suppressed. If desired, use [T][] (that links to T(0 1)) or [T][constant] (that links to T).

    Note that linking to sections in the Hyperspec is done with the CLHS locative and is not subject to the value of this variable.

9.6 Linking to Sections

The following variables control how to generate section numbering, table of contents and navigation links.


    When true, HTML anchors are generated before the headings (e.g. of sections), which allows the table of contents to contain links and also code-like references to sections (like @FOO-MANUAL) to be translated to links with the section title being the name of the link.


    A non-negative integer. In their hierarchy, sections on levels less than this value get numbered in the format of 3.1.2. Setting it to 0 turns numbering off.


    A non-negative integer. Top-level sections are given a table of contents, which includes a nested tree of section titles whose depth is limited by this value. Setting it to 0 turns generation of the table of contents off. If *DOCUMENT-LINK-SECTIONS* is true, then the table of contents will link to the sections.


    If true, then before each heading a line is printed with links to the previous, parent and next section. Needs *DOCUMENT-LINK-SECTIONS* to be on to work.


    If true and the output format is HTML, then headings get a navigation component that consists of links to the previous, parent, next section and a permalink. This component is normally hidden, it is visible only when the mouse is over the heading. Needs *DOCUMENT-LINK-SECTIONS* to be on to work.

9.7 Miscellaneous Variables

  • [variable] *DOCUMENT-URL-VERSIONS* (2 1)

    A list of versions of PAX URL formats to support in the generated documenation. The first in the list is used to generate links.

    PAX emits HTML anchors before the documentation of SECTION(0 1)s (see Linking to Sections) and other things (see Linking to Code). For the function FOO, in the current version (version 2), the anchor is <a id="MGL-PAX:FOO%20FUNCTION"> and its URL will end with #MGL-PAX:FOO%20FUNCTION.

    Note that to make the URL independent of whether a symbol is internal or external to their SYMBOL-PACKAGE, single colon is printed where a double colon would be expected. Package and symbol names are both printed verbatim except for escaping colons and spaces with a backslash. For exported symbols with no funny characters, this coincides with how PRIN1 would print the symbol, while having the benefit of making the URL independent of the Lisp printer's escaping strategy and producing human-readable output for mixed-case symbols. No such promises are made for non-ASCII characters, and their URLs may change in future versions. Locatives are printed with PRIN1.

    Version 1 is based on the more strict HTML4 standard and the id of FOO is "x-28MGL-PAX-3A-3AFOO-20FUNCTION-29". This is supported by Github flavoured Markdown. Version 2 has minimal clutter and is obviously preferred. However, in order not to break external links, by default, both anchors are generated.

    Let's understand the generated Markdown.

    (defun foo (x))
    (document #'foo)
    => ("<a id=\"x-28MGL-PAX-3AFOO-20FUNCTION-29\"></a>
    <a id=\"MGL-PAX:FOO%20FUNCTION\"></a>
    - [function] **FOO** *X*
    (let ((*document-url-versions* '(1)))
      (document #'foo))
    => ("<a id=\"x-28MGL-PAX-3AFOO-20FUNCTION-29\"></a>
    - [function] **FOO** *X*


    Recall that markdown reference style links (like [label][id]) are used for linking to sections and code. It is desirable to have ids that are short to maintain legibility of the generated markdown, but also stable to reduce the spurious diffs in the generated documentation, which can be a pain in a version control system.

    Clearly, there is a tradeoff here. This variable controls how many characters of the md5 sum of the full link id (the reference as a string) are retained. If collisions are found due to the low number of characters, then the length of the hash of the colliding reference is increased.

    This variable has no effect on the HTML generated from markdown, but it can make markdown output more readable.


    When true, some things such as function names and arglists are rendered as bold and italic. In :HTML output, locative types become links to sources (if :SOURCE-URI-FN is provided, see DOCUMENT), and the symbol becomes a self-link for your permalinking pleasure.

    For example, a reference is rendered in markdown roughly as:

      - [function] foo x y

    With this option on, the above becomes:

      - [function] **foo** *x y*

    Also, in HTML **foo** will be a link to that very entry and [function] may turn into a link to sources.


    Determines what *PACKAGE* and *READTABLE* are when working with generating documentation. If true and documentation is generated for a SECTION(0 1) (including its SECTION-ENTRIES), then SECTION-PACKAGE and SECTION-READTABLE of the innermost containing section is used. To eliminate ambiguity [in package ...] messages are printed right after the section heading if necessary. If false, then *PACKAGE* and *READTABLE* are left at the current values.

9.8 Utilities for Generating Documentation

Two convenience functions are provided to serve the common case of having an ASDF system with some readmes and a directory with for the HTML documentation and the default css stylesheet.


    Convenience function to generate two readme files in the directory holding the ASDF-SYSTEM definition. OBJECT is passed on to DOCUMENT. has anchors, links, inline code, and other markup added. Not necessarily the easiest on the eye in an editor, but looks good on github.

    README is optimized for reading in text format. Has no links and less cluttery markup.

    Example usage:

    (update-asdf-system-readmes @pax-manual :mgl-pax)

    Note that *DOCUMENT-URL-VERSIONS* is bound to URL-VERSIONS, that defaults to using the uglier version 1 style of URL for the sake of github.


    Generate pretty HTML documentation for a single ASDF system, possibly linking to github. If UPDATE-CSS-P, copy the CSS style sheet to TARGET-DIR, as well. Example usage:

    (update-asdf-system-html-docs @pax-manual :mgl-pax)

    The same, linking to the sources on github:

      @pax-manual :mgl-pax
        :source-uri-fn ,(make-git-source-uri-fn


    NIL or a non-negative integer. If non-NIL, it overrides *DOCUMENT-MAX-NUMBERING-LEVEL* in dynamic HTML table of contents on the left of the page.

  • [variable] *DOCUMENT-HTML-HEAD* NIL

    NIL or a STRING(0 1) that's going to be included in the of the generated html.


    A list of blocks of links to be displayed on the sidebar on the left, above the table of contents. A block is of the form (&KEY TITLE ID LINKS), where TITLE will be displayed at the top of the block in a HTML DIV with ID, followed by the links. LINKS is a list of (URI LABEL) elements.

9.8.1 Github Workflow

It is generally recommended to commit generated readmes (see UPDATE-ASDF-SYSTEM-READMES), so that users have something to read without reading the code and sites like github can display them.

HTML documentation can also be committed, but there is an issue with that: when linking to the sources (see MAKE-GIT-SOURCE-URI-FN), the commit id is in the link. This means that code changes need to be committed first, and only then can HTML documentation be regenerated and committed in a followup commit.

The second issue is that github is not very good at serving HTMLs files from the repository itself (and chokes on links to the sources).

The recommended workflow is to use gh-pages, which can be made relatively painless with the git worktree command. The gist of it is to make the doc/ directory a checkout of the branch named gh-pages. A good description of this process is Two commits needed still, but it is somewhat less painful.

This way the HTML documentation will be available at http://<username><repo-name>. It is probably a good idea to add sections like the Links section to allow jumping between the repository and the gh-pages site.


    This function is a backward-compatibility wrapper around MAKE-GIT-SOURCE-URI-FN, which supersedes MAKE-GITHUB-SOURCE-URI-FN. All arguments are passed on to MAKE-GIT-SOURCE-URI-FN, leaving URI-FORMAT-STRING at its default, which is suitable for github.


    Return a function suitable as :SOURCE-URI-FN of a page spec (see the PAGES argument of DOCUMENT). The function looks at the source location of the REFERENCE passed to it, and if the location is found, the path is made relative to the root directory of ASDF-SYSTEM and finally an URI pointing to your git forge (such as github) is returned. A warning is signalled whenever the source location lookup fails or if the source location points to a directory not below the directory of ASDF-SYSTEM.

    If GIT-FORE-URI is "" and GIT-VERSION is "master", then the returned URI may look like this:

    If GIT-VERSION is NIL, then an attempt is made to determine to current commit id from the .git in the directory holding ASDF-SYSTEM. If no .git directory is found, then no links to the git forge will be generated.

    URI-FORMAT-STRING is a CL:FORMAT control string for four arguments:



    • the relative path to the file of the source location of the reference,

    • and the line number.

    The default value of URI-FORMAT-STRING is for github. If using a non-standard git forge, such as Sourcehut or Gitlab, simply pass a suitable URI-FORMAT-STRING matching the URI scheme of your forge.

9.8.2 PAX World

PAX World is a registry of documents, which can generate cross-linked HTML documentation pages for all the registered documents.


    Register SECTIONS and PAGE-SPECS under NAME in PAX World. By default, UPDATE-PAX-WORLD generates documentation for all of these.

For example, this is how PAX registers itself:

(defun pax-sections ()
  (list @pax-manual))
(defun pax-pages ()
     (, @pax-manual)
     :source-uri-fn ,(make-git-source-uri-fn
(register-doc-in-pax-world :pax (pax-sections) (pax-pages))


    Generate HTML documentation for all DOCS. Files are created in DIR ((asdf:system-relative-pathname :mgl-pax "world/") by default if DIR is NIL). DOCS is a list of entries of the form (NAME SECTIONS(0 1) PAGE-SPECS). The default for DOCS is all the sections and pages registered with REGISTER-DOC-IN-PAX-WORLD.

    In the absence of :HEADER-FN :FOOTER-FN, :OUTPUT, every spec in PAGE-SPECS is augmented with HTML headers, footers and output location specifications (based on the name of the section).

    If necessary a default page spec is created for every section.

9.9 Overview of Escaping

Let's recap how escaping Codification, downcasing, and Linking to Code works.

  • One backslash in front of a word turns codification off. Use this to prevent codification words such as PAX, which is all uppercase hence codifiable and it names a package hence it is interesting.

  • One backslash right after an opening backtick turns autolinking off.

  • Two backslashes right after an opening backtick turns autolinking and downcasing off. Use this for things that are not Lisp code but which need to be in a monospace font.

In the following examples capital C/D/A letters mark the presence, and a/b/c the absence of codification, downcasing, and autolinking assuming all these features are enabled by *DOCUMENT-UPPERCASE-IS-CODE*. *DOCUMENT-DOWNCASE-UPPERCASE-CODE*, and *DOCUMENT-LINK-CODE*.

DOCUMENT                => [`document`][1234]    (CDA)
\DOCUMENT               => DOCUMENT              (cda)
`\DOCUMENT`             => `document`            (CDa)
`\\DOCUMENT`            => `DOCUMENT`            (CdA)
[DOCUMENT][]            => [`document`][1234]    (CDA)
[\DOCUMENT][]           => [DOCUMENT][1234]      (cdA)
[`\DOCUMENT`][]         => [`document`][1234]    (CDA) *
[`\\DOCUMENT`][]        => [`DOCUMENT`][1234]    (CdA)
[DOCUMENT][dislocated]  => `document`            (CDa)

Note that in the example marked with *, the single backslash, that would normally turn autolinking off, is ignored because it is in an explicit link.

9.10 Document Generation Implementation Notes

Documentation Generation is supported on ABCL, AllegroCL, CLISP, CCL, CMUCL, ECL and SBCL, but their outputs may differ due to the lack of some introspective capability. SBCL generates complete output. Compared to that, the following are not supported:

  • COMPILER-MACRO docstrings on ABCL, AllegroCL, CCL, ECL,

  • DEFTYPE lambda lists on ABCL, AllegroCL, CLISP, CCL, CMUCL, ECL,

  • default values in MACRO lambda lists on AllegroCL,

  • METHOD-COMBINATION(0 1) docstrings on ABCL, AllegroCL.

10 Transcripts

What are transcripts for? When writing a tutorial, one often wants to include a REPL session with maybe a few defuns and a couple of forms whose output or return values are shown. Also, in a function's docstring an example call with concrete arguments and return values speaks volumes. A transcript is a text that looks like a repl session, but which has a light markup for printed output and return values, while no markup (i.e. prompt) for Lisp forms. PAX transcripts may include output and return values of all forms, or only selected ones. In either case, the transcript itself can be easily generated from the source code.

The main worry associated with including examples in the documentation is that they tend to get out-of-sync with the code. This is solved by being able to parse back and update transcripts. In fact, this is exactly what happens during documentation generation with PAX. Code sections tagged cl-transcript are retranscribed and checked for inconsistency (that is, any difference in output or return values). If the consistency check fails, an error is signalled that includes a reference to the object being documented.

Going beyond documentation, transcript consistency checks can be used for writing simple tests in a very readable form. For example:

(+ 1 2)
=> 3

(values (princ :hello) (list 1 2))
=> (1 2)

All in all, transcripts are a handy tool especially when combined with the Emacs support to regenerate them and with PYTHONIC-STRING-READER's triple-quoted strings, that allow one to work with nested strings with less noise. The triple-quote syntax can be enabled with:

(in-readtable pythonic-string-syntax)


10.2 Transcribing with Emacs

Typical transcript usage from within Emacs is simple: add a lisp form to a docstring or comment at any indentation level. Move the cursor right after the end of the form as if you were to evaluate it with C-x C-e. The cursor is marked by #\^:

This is part of a docstring.

(values (princ :hello) (list 1 2))^

Note that the use of fenced code blocks with the language tag cl-transcript is only to tell PAX to perform consistency checks at documentation generation time.

Now invoke the elisp function mgl-pax-transcribe where the cursor is and the fenced code block from the docstring becomes:

(values (princ :hello) (list 1 2))
=> (1 2)

Then you change the printed message and add a comment to the second return value:

(values (princ :hello-world) (list 1 2))
=> (1
    ;; This value is arbitrary.

When generating the documentation you get a TRANSCRIPTION-CONSISTENCY-ERROR because the printed output and the first return value changed so you regenerate the documentation by marking the region of bounded by #\| and the cursor at #\^ in the example:

|(values (princ :hello-world) (list 1 2))
=> (1
    ;; This value is arbitrary.

then invoke the elisp function mgl-pax-retranscribe-region to get:

(values (princ :hello-world) (list 1 2))
=> (1
    ;; This value is arbitrary.

Note how the indentation and the comment of (1 2) was left alone but the output and the first return value got updated.

Alternatively, C-u 1 mgl-pax-transcribe will emit commented markup:

(values (princ :hello) (list 1 2))
;=> :HELLO
;=> (1 2)

C-u 0 mgl-pax-retranscribe-region will turn commented into non-commented markup. In general, the numeric prefix argument is the index of the syntax to be used in MGL-PAX:*TRANSCRIBE-SYNTAXES*. Without a prefix argument mgl-pax-retranscribe-region will not change the markup style.

Finally, not only do both functions work at any indentation level, but in comments too:

;;;; (values (princ :hello) (list 1 2))
;;;; .. HELLO
;;;; => :HELLO
;;;; => (1 2)

Transcription support in emacs can be enabled by loading src/transcribe.el.

10.3 Transcript API


    Read forms from INPUT and write them (iff ECHO) to OUTPUT followed by any output and return values produced by calling EVAL on the form. INPUT can be a stream or a string, while OUTPUT can be a stream or NIL in which case transcription goes into a string. The return value is the OUTPUT stream or the string that was constructed.

    A simple example is this:

    (transcribe "(princ 42) " nil)
    => "(princ 42)
    .. 42
    => 42

    However, the above may be a bit confusing since this documentation uses TRANSCRIBE markup syntax in this very example, so let's do it differently. If we have a file with these contents:

    (values (princ 42) (list 1 2))

    it is transcribed to:

    (values (princ 42) (list 1 2))
    .. 42
    => 42
    => (1 2)

    Output to all standard streams is captured and printed with the :OUTPUT prefix (".."). The return values above are printed with the :READABLE prefix ("=>"). Note how these prefixes are always printed on a new line to facilitate parsing.


    TRANSCRIBE is able to parse its own output. If we transcribe the previous output above, we get it back exactly. However, if we remove all output markers, leave only a placeholder value marker and pass :UPDATE-ONLY T with source:

    (values (princ 42) (list 1 2))

    we get this:

    (values (princ 42) (list 1 2))
    => 42
    => (1 2)

    With UPDATE-ONLY, the printed output of a form is only transcribed if there were output markers in the source. Similarly, with UPDATE-ONLY, return values are only transcribed if there were value markers in the source.

    No Output/Values

    If the form produces no output or returns no values, then whether or not output and values are transcribed is controlled by INCLUDE-NO-OUTPUT and INCLUDE-NO-VALUE, respectively. By default, neither is on so:


    is transcribed to


    With UPDATE-ONLY true, we probably wouldn't like to lose those markers since they were put there for a reason. Hence, with UPDATE-ONLY, INCLUDE-NO-OUTPUT and INCLUDE-NO-VALUE default to true. So with UPDATE-ONLY the above example is transcribed to:

    => ; No value

    where the last line is the :NO-VALUE prefix.

    Consistency Checks

    If CHECK-CONSISTENCY is true, then TRANSCRIBE signals a continuable TRANSCRIPTION-OUTPUT-CONSISTENCY-ERROR whenever a form's output as a string is different from what was in INPUT, provided that INPUT contained the output. Similary, for values, a continuable TRANSCRIPTION-VALUES-CONSISTENCY-ERROR is signalled if a value read from the source does not print as the as the value returned by EVAL. This allows readable values to be hand-indented without failing consistency checks:

    (list 1 2)
    => ;; This is commented, too.
          ;; Funny indent.

    See Transcript Consistency Checking for the full picture.

    Unreadable Values

    The above scheme involves READ, so consistency of unreadable values cannot be treated the same. In fact, unreadable values must even be printed differently for transcribe to be able to read them back:

    (defclass some-class () ())
    (defmethod print-object ((obj some-class) stream)
      (print-unreadable-object (obj stream :type t)
        (format stream \"~%~%end\")))
    (make-instance 'some-class)
    ==> #<SOME-CLASS 
    --> end>

    where "==>" is the :UNREADABLE prefix and "-->" is the :UNREADABLE-CONTINUATION prefix. As with outputs, a consistency check between an unreadable value from the source and the value from EVAL is performed with STRING= by default. That is, the value from EVAL is printed to a string and compared to the source value. Hence, any change to unreadable values will break consistency checks. This is most troublesome with instances of classes with the default PRINT-OBJECT method printing the memory address. See @ no remedy for that, except for customizing PRINT-OBJECT or not transcribing that kind of stuff.


    If an ERROR condition is signalled, the error is printed to the output and no values are returned.

      (print "hello")
      (error "no greeting"))
    .. "hello" 
    .. debugger invoked on SIMPLE-ERROR:
    ..   no greeting

    To keep the textual representation somewhat likely to be portable, the printing is done with (FORMAT T "#<~S ~S>" (TYPE-OF ERROR) (PRINC-TO-STRING ERROR)). SIMPLE-CONDITIONs are formatted to strings with SIMPLE-CONDITION-FORMAT-CONTROL and SIMPLE-CONDITION-FORMAT-ARGUMENTS.


    Finally, a transcript may employ different syntaxes for the output and values of different forms. When INPUT is read, the syntax for each form is determined by trying to match all prefixes from all syntaxes in INPUT-SYNTAXES against a line. If there are no output or values for a form in INPUT, then the syntax remains undetermined.

    When OUTPUT is written, the prefixes to be used are looked up in DEFAULT-SYNTAX of OUTPUT-SYNTAXES, if DEFAULT-SYNTAX is not NIL. If DEFAULT-SYNTAX is NIL, then the syntax used by the same form in the INPUT is used or (if that could not be determined) the syntax of the previous form. If there was no previous form, then the first syntax if OUTPUT-SYNTAXES is used.

    To produce a transcript that's executable Lisp code, use :DEFAULT-SYNTAX :COMMENTED-1:

    (make-instance 'some-class)
    ;==> #<SOME-CLASS
    ;--> end>
    (list 1 2)
    ;=> (1
    ;->    2)

    To translate the above to uncommented syntax, use :DEFAULT-SYNTAX :DEFAULT. If DEFAULT-SYNTAX is NIL (the default), the same syntax will be used in the output as in the input as much as possible.


    The default value of TRANSCRIBE's CHECK-CONSISTENCY argument.

  • [variable] *TRANSCRIBE-SYNTAXES* ((:DEFAULT (:OUTPUT "..") (:NO-VALUE "=> ; No value") (:READABLE "=>") (:UNREADABLE "==>") (:UNREADABLE-CONTINUATION "-->")) (:COMMENTED-1 (:OUTPUT ";..") (:NO-VALUE ";=> ; No value") (:READABLE ";=>") (:READABLE-CONTINUATION ";->") (:UNREADABLE ";==>") (:UNREADABLE-CONTINUATION ";-->")) (:COMMENTED-2 (:OUTPUT ";;..") (:NO-VALUE ";;=> ; No value") (:READABLE ";;=>") (:READABLE-CONTINUATION ";;->") (:UNREADABLE ";;==>") (:UNREADABLE-CONTINUATION ";;-->")))

    The default syntaxes used by TRANSCRIBE for reading and writing lines containing output and values of an evaluated form.

    A syntax is a list of of the form (SYNTAX-ID &REST PREFIXES) where PREFIXES is a list of (PREFIX-ID PREFIX-STRING) elements. For example the syntax :COMMENTED-1 looks like this:

     (:output ";..")
     (:no-value ";=>  No value")
     (:readable ";=>")
     (:readable-continuation ";->")
     (:unreadable ";==>")
     (:unreadable-continuation ";-->"))

    All of the above prefixes must be defined for every syntax except for :READABLE-CONTINUATION. If that's missing (as in the :DEFAULT syntax), then the following value is read with READ and printed with PRIN1 (hence no need to mark up the following lines).

    When writing, an extra space is added automatically if the line to be prefixed is not empty. Similarly, the first space following the prefix is discarded when reading.

    See TRANSCRIBE for how the actual syntax to be used is selected.


    Signaled (with CERROR) by TRANSCRIBE when invoked with :CHECK-CONSISTENCY and the output of a form is not the same as what was parsed.


    Signaled (with CERROR) by TRANSCRIBE when invoked with :CHECK-CONSISTENCY and the values of a form are inconsistent with their parsed representation.

10.4 Transcript Consistency Checking

The main use case for consistency checking is detecting out-of-date examples in documentation, although using it for writing tests is also a possiblity. Here, we focus on the former.

When a markdown code block tagged cl-transcript is processed during Generating Documentation, the code in it is replaced with the output of with (TRANSCRIBE <CODE> NIL :UPDATE-ONLY T :CHECK-CONSISTENCY T). Suppose we have the following example of the function GREET, that prints hello and returns 7.

.. hello
=> 7

Now, if we change GREET to print or return something else, a TRANSCRIPTION-CONSISTENCY-ERROR will be signalled during documentation generation. Then we may fix the documentation or CONTINUE from the error.

By default, comparisons of previous to current ouput, readable and unreadable return values are performed with STRING=, EQUAL, and STRING=, respectively, which is great in the simple case. Non-determinism aside, exact matching becomes brittle as soon as the notoriously unportable pretty printer is used or when unreadable objects are printed with their #<> syntax, especially when PRINT-UNREADABLE-OBJECT is used with :IDENTITY T.

10.4.1 Finer-grained Consistency Checks

To get around this problem, consistency checking of output, readable and unreadable values can be customized individually by supplying TRANSCRIBE with a CHECK-CONSISTENCY argument like ((:OUTPUT <OUTPUT-CHECK>) (:READABLE <READABLE-CHECK>) (:UNREADABLE <UNREADABLE-CHECK>)). In this case, <OUTPUT-CHECK> may be NIL, T, or a function designator.

  • If it's NIL or there is no :OUTPUT entry in the list, then the output is not checked for consistency.

  • If it's T, then the outputs are compared with the default, STRING=.

  • If it's a function designator, then it's called with two strings and must return whether they are consistent with each other.

The case of <READABLE-CHECK> and <UNREADABLE-CHECK> is similar.

Code blocks tagged cl-transcript can take arguments, which they pass on to TRANSCRIBE. The following shows how to check only the output.

```cl-transcript (:check-consistency ((:output t)))
(error "Oh, no.")
.. debugger invoked on SIMPLE-ERROR:
..   Oh, no.

(make-condition 'simple-error)
==> #<SIMPLE-ERROR {1008A81533}>

10.4.2 Controlling the Dynamic Environment

The dynamic enviroment in which forms in the transcript are evaluated can be controlled via the :DYNENV argument of cl-transcript.

```cl-transcript (:dynenv my-transcript)

In this case, instead of calling TRANSCRIBE directly, the call will be wrapped in a function of no arguments and passed to the function MY-TRANSCRIPT, which establishes the desired dynamic environment and calls its argument. The following definition of MY-TRANSCRIPT simply packages up oft-used settings to TRANSCRIBE.

(defun my-transcript (fn)
  (let ((*transcribe-check-consistency*
          '((:output my-transcript-output=)
            (:readable equal)
            (:unreadable nil))))
    (funcall fn)))

(defun my-transcript-output= (string1 string2)
  (string= (my-transcript-normalize-output string1)
           (my-transcript-normalize-output string2)))

(defun my-transcript-normalize-output (string)
  (squeeze-whitespace (delete-trailing-whitespace (delete-comments string))))

A more involved solution could rebind global variables set in transcripts, unintern symbols created or even create a temporary package for evaluation.

10.4.3 Utilities for Consistency Checking


    Replace consecutive whitespace characters with a single space in STRING. This is useful to do undo the effects of pretty printing when building comparison functions for TRANSCRIBE.


    Delete whitespace characters after the last non-whitespace character in each line in STRING.


    For each line in STRING delete the rest of the line after and including the first occurrence of PATTERN. On changed lines, delete trailing whitespace too. Let's define a comparison function:

    (defun string=/no-comments (string1 string2)
      (string= (delete-comments string1) (delete-comments string2)))

    And use it to check consistency of output:

      ```cl-transcript (:check-consistency ((:output string=/no-comments)))
      (format t "hello~%world")
      .. hello     ; This is the first line.
      .. world     ; This is the second line.

    Just to make sure the above example works, here it is without the being quoted.

    (format t "hello~%world")
    .. hello     ; This is the first line.
    .. world     ; This is the second line.

11 Writing Extensions

11.1 Adding New Object Types

One may wish to make the DOCUMENT function and M-. navigation work with new object types. DOCUMENT can be extended by defining a DOCUMENT-OBJECT method specialized on that type. To allow these objects to be referenced from DEFSECTION, LOCATE-OBJECT method is to be defined. If there are multiple equivalent references possible for the same thing, then CANONICAL-REFERENCE must be specialized. For the DOCSTRING locative to work on the new type, a DOCSTRING method is needed. For M-. FIND-SOURCE can be specialized. Finally, EXPORTABLE-LOCATIVE-TYPE-P may be overridden if exporting does not makes sense. Here is how all this is done for ASDF:SYSTEM:

(define-locative-type asdf:system ()
  "Refers to an asdf system. The generated documentation will include
  meta information extracted from the system definition. This also
  serves as an example of a symbol that's not accessible in the
  current package and consequently is not exported.


(defmethod locate-object (name (locative-type (eql 'asdf:system))
  (or (and (endp locative-args)
           ;; ASDF:FIND-SYSTEM is slow as hell.
           (asdf:find-system (string-downcase (string name)) nil))
      (locate-error "~S does not name an asdf system." name)))

(defmethod canonical-reference ((system asdf:system))
  (make-reference (character-string (slot-value system 'asdf::name))

;;; For testing
(defvar *omit-asdf-slots* nil)

(defmethod document-object ((system asdf:system) stream)
  (with-heading (stream system
                        (format nil "~A \\ASDF System"
                                 (slot-value system 'asdf::name))))
    (flet ((foo (name fn &key type)
             (let ((value (funcall fn system)))
               (when (and value (not (equal value "")))
                 (case type
                    (format stream "- ~A: [~A](~A)~%" name value value))
                    (format stream "- ~A: [~A](mailto:~A)~%"
                            name value value))
                    (format stream "- ~A: [~A](~A)"
                            name (first value) (second value)))
                    (format stream "- ~A: " name)
                    (document-docstring value stream
                                        :indentation "  "
                                        :exclude-first-line-p t
                                        :paragraphp nil)
                    (terpri stream))
                    (format stream "- ~A: ~A~%" name value)))))))
      (unless *omit-asdf-slots*
        (foo "Version" 'asdf/component:component-version)
        (foo "Description" 'asdf/system:system-description :type :docstring)
        (foo "Long Description" 'asdf/system:system-long-description
             :type :docstring)
        (foo "Licence" 'asdf/system:system-licence)
        (foo "Author" 'asdf/system:system-author)
        (foo "Maintainer" 'asdf/system:system-maintainer)
        (foo "Mailto" 'asdf/system:system-mailto :type :mailto)
        (foo "Homepage" 'asdf/system:system-homepage :type :link)
        (foo "Bug tracker" 'asdf/system:system-bug-tracker :type :link)
        (foo "Source control" 'asdf/system:system-source-control
             :type :source-control)
        (terpri stream)))))

(defmethod docstring ((system asdf:system))

(defmethod find-source ((system asdf:system))
    (:file ,(namestring (asdf/system:system-source-file system)))
    (:position 1)
    (:snippet "")))

(add-locative-to-source-search-list 'asdf:system)


    Declare LOCATIVE-TYPE as a LOCATIVE. One gets two things in return: first, a place to document the format and semantics of LOCATIVE-TYPE (in LAMBDA-LIST and DOCSTRING); second, being able to reference (LOCATIVE-TYPE LOCATIVE). For example, if you have:

    (define-locative-type variable (&optional initform)
      "Dummy docstring.")

    then (VARIABLE LOCATIVE) refers to this form.


    Define ALIAS as a locative equivalent to LOCATIVE-TYPE (both SYMBOLs). The following example shows how to make docstrings read more naturally by defining an alias.

    (defclass my-string ()
    (defgeneric my-string (obj)
      (:documentation "Convert OBJ to MY-STRING."))
    ;;; This version of FOO has a harder to read docstring because
    ;;; it needs to disambiguate the MY-STRING reference.
    (defun foo (x)
      "FOO takes and argument X, a [MY-STRING][class] object.")
    ;;; Define OBJECT as an alias for the CLASS locative.
    (define-locative-alias object class)
    ;;; Note how no explicit link is needed anymore.
    (defun foo (x)
      "FOO takes an argument X, a MY-CLASS object.")


    Return the object to which OBJECT and the locative refer. Signal a LOCATE-ERROR condition by calling the LOCATE-ERROR function if the lookup fails. If a REFERENCE is returned, then it must be canonical in the sense that calling CANONICAL-REFERENCE on it will return the same reference. Don't call this function directly. It serves only to extend LOCATE.


    Return a list of objects representing all things to be documented in a (DOCUMENT OBJECT) call. For a SECTION(0 1) this is simply the union of references reachable from references in its SECTION-ENTRIES. The returned objects can be anything provided that CANONICAL-REFERENCE works on them. The list need not include OBJECT itself.

    One only has to specialize this for new container-like objects. Its reference delegate is LOCATE-AND-COLLECT-REACHABLE-OBJECTS.

  • [generic-function] DOCUMENT-OBJECT OBJECT STREAM

    Write OBJECT (and its references recursively) in *FORMAT* to STREAM in markdown format. Add methods specializing on OBJECT to customize the output of DOCUMENT. Its reference delegate is LOCATE-AND-DOCUMENT. This function is for extension, don't call it directly.

  • [generic-function] DOCSTRING OBJECT

    Return the docstring from the definition of OBJECT with leading indentation stripped. This function serves a similar purpose as CL:DOCUMENTATION, but it works with first-class objects when there is one for the corresponding definition, and with REFERENCEs when there is not. Its reference delegate is LOCATE-DOCSTRING.

    DOCSTRING is used in the implementation of the DOCSTRING locative. Some things such as ASDF:SYSTEMs and DECLARATION(0 1)s have no docstrings. Notably SECTION(0 1)s don't provide access to docstrings.

  • [generic-function] FIND-SOURCE OBJECT

    Return the Swank source location for OBJECT. It is called by LOCATE-DEFINITIONS-FOR-EMACS, which lies behind the M-. extension (see Navigating Sources in Emacs). Its reference delegate is LOCATE-AND-FIND-SOURCE.

    If successful, the return value should look like one of these:

      (:FILE "/home/melisgl/own/mgl-pax/src/pax.lisp")
      (:POSITION 3303) NIL)
      (:FILE "/home/melisgl/own/mgl-pax/src/pax.lisp")
      (:OFFSET 1 3303) NIL)
      (:FILE "/home/melisgl/own/mgl-pax/src/pax.lisp")

    The NIL above is the source snippet, which is optional. Note that position 1 is the first character in :FILE. If unsuccessful, the return value is like:

    (:error "Unknown source location for SOMETHING")


    Return true iff SYMBOL is to be exported from PACKAGE when it occurs in a DEFSECTION as a reference with LOCATIVE-TYPE and LOCATIVE-ARGS. SYMBOL is accessible in PACKAGE.

    The default method calls EXPORTABLE-LOCATIVE-TYPE-P with LOCATIVE-TYPE and ignores the other arguments.

    For example, to prevent SECTION(0 1)s from being export from the MGL-PAX package, the following method is defined.

    (defmethod exportable-reference-p ((package (eql (find-package 'mgl-pax)))
                                       symbol (locative-type (eql 'section))


    Return true iff symbols in references with LOCATIVE-TYPE are to be exported by default when they occur in a DEFSECTION. The default method returns T, while the methods for SECTION(0 1), GLOSSARY-TERM(0 1), PACKAGE(0 1), ASDF:SYSTEM, METHOD(0 1) and INCLUDE return NIL.

    This function is called by the default method of EXPORTABLE-REFERENCE-P to decide what symbols DEFSECTION shall export when its EXPORT argument is true.

11.2 Reference Based Extensions

Let's see how to extend DOCUMENT and M-. navigation if there is no first-class object to represent the definition of interest. Recall that LOCATE returns a REFERENCE object in this case. The generic functions that we have specialized in Adding New Object Types have reference delegates, which can be specialized based on LOCATIVE-TYPE. Here is how the VARIABLE locative is defined:

(define-locative-type variable (&optional initform)
  """Refers to a global special variable. INITFORM, or if not specified,
  the global value of the variable is included in the documentation.

;;; A REFERENCE is returned because there is no such type as VARIABLE. (locate 'FORMAT 'variable) ==> #<REFERENCE FORMAT VARIABLE>

see *FORMAT*. Note that *FORMAT* is unbound. If the variable is
BOUNDP, then its _current_ value is included in the documentation.
See *DOCUMENT-LINK-CODE* for an example output. To override the
current value, `INITFORM` may be provided. This is particulary
useful if the value of the variable is something undesirable such as
`\\#<MY-CLASS {100171ED93}>`.""")

(defmethod locate-object (symbol (locative-type (eql 'variable)) locative-args)
(unless (<= (length locative-args) 1)
  (locate-error "The lambda list of the VARIABLE locative is ~
                 (&OPTIONAL INITFORM)."))
(make-reference symbol (cons locative-type locative-args)))

(defmethod locate-and-document (symbol (locative-type (eql 'variable))
                              locative-args stream)
(destructuring-bind (&optional (initform nil initformp)) locative-args
  (let ((arglist (multiple-value-bind (value unboundp)
                     (symbol-global-value symbol)
                   (when (or initformp (not unboundp))
                     (let ((*print-pretty* t))
                       (prin1-to-markdown (if initformp
    (documenting-reference (stream :arglist arglist)
      (document-docstring (documentation* symbol 'variable) stream)))))

(defmethod locate-docstring (symbol (locative-type (eql 'variable))
(declare (ignore locative-args))
(documentation* symbol 'variable))

(defmethod locate-and-find-source (symbol (locative-type (eql 'variable))
(declare (ignore locative-args))
(find-definition symbol 'variable))

  • [glossary-term] reference delegate

    CANONICAL-REFERENCE, COLLECT-REACHABLE-OBJECTS, DOCUMENT-OBJECT, DOCSTRING, and FIND-SOURCE delegate dealing with REFERENCES to another generic function, one each, which is called their reference delegate. Each of these delegator functions invokes its delegate when a REFERENCE is passed to it (as its OBJECT argument), or there is no method specialized for its arguments, in which case it uses the CANONICAL-REFERENCE.

    The net effect is that is that it is sufficient to specialize either the delegator for a first-class object or the delegate for a new locative type.


    This is the reference delegate of CANONICAL-REFERENCE. The default method calls LOCATE-OBJECT with the three arguments. If LOCATE-OBJECT returns a REFERENCE, then that's taken to be the canonical reference and is returned, else CANONICAL-REFERENCE is invoked with the returned object.

We have covered the basic building blocks of reference based extensions. Now let's see how the obscure DEFINE-SYMBOL-LOCATIVE-TYPE and DEFINE-DEFINER-FOR-SYMBOL-LOCATIVE-TYPE macros work together to simplify the common task of associating definition and documentation with symbols in a certain context.


    Similar to DEFINE-LOCATIVE-TYPE but it assumes that all things locatable with LOCATIVE-TYPE are going to be just symbols defined with a definer defined with DEFINE-DEFINER-FOR-SYMBOL-LOCATIVE-TYPE. It is useful to attach documentation and source location to symbols in a particular context. An example will make everything clear:

    (define-symbol-locative-type direction ()
      "A direction is a symbol. (After this `M-.` on `DIRECTION LOCATIVE`
      works and it can also be included in DEFSECTION forms.)")
    (define-definer-for-symbol-locative-type define-direction direction
      "With DEFINE-DIRECTION one can document what a symbol means when
      interpreted as a direction.")
    (define-direction up ()
      "UP is equivalent to a coordinate delta of (0, -1).")

    After all this, (UP DIRECTION) refers to the DEFINE-DIRECTION form above.


    Define a macro with NAME which can be used to attach documentation, a lambda-list and source location to a symbol in the context of LOCATIVE-TYPE. The defined macro's arglist is (SYMBOL LAMBDA-LIST &OPTIONAL DOCSTRING). LOCATIVE-TYPE is assumed to have been defined with DEFINE-SYMBOL-LOCATIVE-TYPE.

11.3 Extending DOCUMENT

The following utilities are for writing new DOCUMENT-OBJECT and LOCATE-AND-DOCUMENT methods, which emit markdown.

  • [variable] *FORMAT*

    Bound by DOCUMENT, this allows markdown output to depend on the output format.


    Write a markdown heading with TITLE to STREAM. Nested WITH-HEADINGs produce nested headings. If *DOCUMENT-LINK-SECTIONS*, generate anchors based on the CANONICAL-REFERENCE of OBJECT. LINK-TITLE-TO behaves like the LINK-TITLE-TO argument of DEFSECTION.


    Write REFERENCE to STREAM as described in *DOCUMENT-MARK-UP-SIGNATURES*, and establish REFERENCE as a local reference. Unless ARGLIST is NIL or :NOT-AVAILABLE, it is printed after the name of object of REFERENCE.

    If ARGLIST is a list, then it is must be a lambda list and is printed without the outermost parens and with the package names removed from the argument names.

    If ARGLIST is a string, then it is printed without ESCAPE-MARKDOWN.


    Process and DOCSTRING to STREAM, stripping indentation from it, performing Codification and Linking to Code, finally prefixing each line with INDENTATION. The prefix is not added to the first line if EXCLUDE-FIRST-LINE-P. If PARAGRAPHP, then add a newline before and after the output.


    A small wrapper around CL:DOCUMENTATION to smooth over differences between implementations.


    Construct a new string from STRING by adding a backslash before each special markdown character:


11.4 Extending FIND-SOURCE

The following utilities are for writing new FIND-SOURCE and LOCATE-AND-FIND-SOURCE methods. Their locative arguments are translated to Swank dspecs, and it is an error if there is no translation. In general, Swank supports Common Lisp definitions (hence the VARIABLE and FUNCTION(0 1 2) locatives, for example) but not PAX- and user-defined additions (e.g. SECTION(0 1), ASDF:SYSTEM).


    Return a Swank source location for a definition of OBJECT. Try forming references with OBJECT and one of LOCATIVES. Stop at the first locative with which a definition is found, and return its location. If no location was found, then return the usual Swank (:ERROR ...). The implementation is based on the rather expensive SWANK-BACKEND:FIND-DEFINITIONS function.


    Like FIND-DEFINITION, but tries to get the definition of OBJECT (for example a FUNCTION(0 1 2) or METHOD(0 1) object) with the fast but not widely supported SWANK-BACKEND:FIND-SOURCE-LOCATION before calling the much slower but more complete SWANK-BACKEND:FIND-DEFINITIONS.

11.5 Sections

SECTION objects rarely need to be dissected since DEFSECTION and DOCUMENT cover most needs. However, it is plausible that one wants to subclass them and maybe redefine how they are presented.


    The name of the global variable whose value is this SECTION(0 1) object.


    A markdown string or NIL. Used in generated documentation.


    A REFERENCE or NIL. Used in generated documentation.


    A list of markdown docstrings and REFERENCE objects in the order they occurred in DEFSECTION.

11.6 Glossary Terms

GLOSSARY-TERM objects rarely need to be dissected since DEFINE-GLOSSARY-TERM and DOCUMENT cover most needs. However, it is plausible that one wants to subclass them and maybe redefine how they are presented.

  • [class] GLOSSARY-TERM

    DEFINE-GLOSSARY-TERM instantiates a GLOSSARY-TERM with its NAME and TITLE arguments.


    The name of the global variable whose value is this GLOSSARY-TERM(0 1) object.


    A markdown string or NIL. Used in generated documentation.

[generated by MGL-PAX]


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