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PAX Manual

Table of Contents

[in package MGL-PAX with nicknames PAX]

1 mgl-pax ASDF System Details

2 Links

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

3 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As a user, I frequently run into documentation that's incomplete and out of date, so I tend to stay in the editor and explore the code by jumping around with SLIME's M-..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 Programming weenie turned inside out. The original prototype which did almost everything I wanted was this:

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

Armed with DEFSECTION, I soon found myself organizing code following the flow of user level documentation and relegated comments to implementational details entirely. However, some portions of DEFSECTION docstrings were just listings of all the functions, macros and variables related to the narrative, and this list was effectively 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 @mgl-pax-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.

4 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 Emacs Integration. 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 yet. Code is first, code must look pretty, documentation is code.

In typical use, PAX packages have no :EXPORT's defined. Instead the DEFINE-PACKAGE form gets a docstring which may mention section names (defined with DEFSECTION). When the code is loaded into the lisp, pressing M-. in SLIME on the name of the section will take you there. Sections can also refer to other sections, packages, functions, etc and you can keep exploring.

Here is an example of how it all works together:

(mgl-pax:define-package :foo-random
  (:documentation "This package provides various utilities for
  (: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 which."
  (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)

Generating documentation in a very stripped down markdown format is easy:

(describe @foo-random-manual)

For this example, the generated markdown would look like this:

# Foo Random manual

###### \[in package FOO-RANDOM\]
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 which.



Hey we can also print states!


- [variable] *FOO-STATE* #<FOO-RANDOM-STATE >

    Much like *RANDOM-STATE* but uses the FOO algorithm.


    Return a random number from a zero mean normal distribution with


    Return a random number from the between 0 and LIMIT (exclusive)
    uniform distribution.

## Examples

Let's see the transcript of a real session of someone working
with FOO:

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

(make-instance 'foo-random-state)


More fancy markdown or HTML output with automatic markup and linking of uppercase symbol names found in docstrings, section numbering, table of contents, etc is possible by calling the DOCUMENT function.

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.

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. See Locative Types.

The transcript in the code block tagged with cl-transcript is automatically checked for up-to-dateness. See Transcripts.

5 Emacs Integration

Integration into SLIME's M-. (slime-edit-definition) allows one to visit the source location of the thing that's identified by a symbol 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.

Note that the this feature is implemented in terms of SWANK-BACKEND:FIND-SOURCE-LOCATION and SWANK-BACKEND:FIND-DEFINITIONS whose support varies across the Lisp implementations.

In the following examples, pressing M-. when the cursor is on one of the characters of FOO or just after FOO, 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 this 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 adding this to your Emacs initialization file (or loading src/pax.el):

;;; MGL-PAX M-. integration

(defun slime-edit-locative-definition (name &optional where)
  (or (slime-locate-definition name (slime-locative-before))
      (slime-locate-definition name (slime-locative-after))
      (slime-locate-definition name (slime-locative-after-in-brackets))
      ;; support "foo function" and "function foo" syntax in
      ;; interactive use
      (let ((pos (cl-position ?\s name)))
        (when pos
          (or (slime-locate-definition (cl-subseq name 0 pos)
                                       (cl-subseq name (1+ pos)))
              (slime-locate-definition (cl-subseq name (1+ pos))
                                       (cl-subseq name 0 pos)))))))

(defun slime-locative-before ()
  (ignore-errors (save-excursion

(defun slime-locative-after ()
  (ignore-errors (save-excursion

(defun slime-locative-after-in-brackets ()
  (ignore-errors (save-excursion
                   (skip-chars-forward "`" (+ (point) 1))
                   (when (and (= 1 (skip-chars-forward "\\]" (+ (point) 1)))
                              (= 1 (skip-chars-forward "\\[" (+ (point) 1))))
                      (progn (search-forward "]" nil (+ (point) 1000))
                             (1- (point))))))))

(defun slime-locate-definition (name locative)
  (when locative
    (let ((location
            ;; Silently fail if mgl-pax is not loaded.
            `(cl:when (cl:find-package :mgl-pax)
                        (cl:symbol-name :locate-definition-for-emacs) :mgl-pax)
                       ,name ,locative)))))
      (when (and (consp location)
                 (not (eq (car location) :error)))
         (list (make-slime-xref :dspec `(,name)
                                :location location))
         "dummy name"

(add-hook 'slime-edit-definition-hooks 'slime-edit-locative-definition)

6 Basics

Now let's examine the most important pieces in detail.


    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. Docstrings are arbitrary strings in markdown format, references are defined in the form:

      (symbol 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)).

    A locative in a reference can either be a symbol or it can be a list whose CAR is a symbol. In either case, the symbol is the called the type of the locative while the rest of the elements are the locative arguments. See Locative Types for the list of locative types available out of the box.

    The same symbol can occur multiple times in a reference, typically with different locatives, but this is not required.

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

    If EXPORT is true (the default), the referenced symbols and NAME are candidates for exporting. A candidate symbol is exported if

    • it is accessible in PACKAGE (it's not OTHER-PACKAGE:SOMETHING) and

    • there is a reference to it in the section being defined with a locative whose type is approved by EXPORTABLE-LOCATIVE-TYPE-P.

    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 non-marked-up string 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 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.


    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 objects like (DOCUMENT @MGL-PAX-MANUAL), but it supports all kinds of objects for which DOCUMENT-OBJECT is defined. To look up the documentation of function DOCUMENT:

      (document #'document)

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

      (document (list @cube-manual @mat-manual))

    Note that not only first class objects can have documentation. For instance, variables and deftypes are not represented by objects. That's why CL:DOCUMENTATION has a DOC-TYPE argument. DOCUMENT does not have anything like that, instead it relies on REFERENCE objects to carry the extra information. We are going to see later how references and locatives work. Until then, here is an example on how to look up the documentation of type FOO:

      (document (locate 'foo 'type))

    One can call DESCRIBE on SECTION objects to get documentation in markdown format with less markup than the default. See DESCRIBE-OBJECT (METHOD () (SECTION T)).

    There are quite a few special variables that affect how output is generated, see Documentation Printer Variables.

    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 contained in one of its :OBJECTS in the sense of COLLECT-REACHABLE-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 as arguments 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.

    If no PAGES are specified, DOCUMENT returns a single pathname, string or stream object according to the value of the STREAM argument.

    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 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-GITHUB-SOURCE-URI-FN.

    PAGES may look something like this:

    `((;; The section about SECTIONs and everything below it ...
       :objects (, @mgl-pax-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 @MGL-PAX-EXTENSION-API section and everything reachable
      ;; from it ...
      (:objects (, @mgl-pax-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 (, @mgl-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))

7 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. 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 cluttery markup.

    Example usage:

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


    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 @mgl-pax-manual :mgl-pax)

    The same, linking to the sources on github:

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


    A list of blocks of links to be display 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.

7.1 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-GITHUB-SOURCE-URI-FN), the commit id is in the link. This means that code changes need to be committed first, then HTML documentation 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 workflow 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 section like the Links section to allow jumping between the repository and the gh-pages site.


    Return a function suitable as :SOURCE-URI-FN of a page spec (see the PAGES argument of DOCUMENT). The function looks 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 github is returned. The URI looks like this:

    "master" in the above link comes from GIT-VERSION.

    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 github will be generated.

    A separate warning is signalled whenever source location lookup fails or if the source location points to a directory not below the directory of ASDF-SYSTEM.

7.2 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 @mgl-pax-manual))
(defun pax-pages ()
     :source-uri-fn ,(make-github-source-uri-fn
(register-doc-in-pax-world :mgl-pax (pax-sections) (pax-pages))


    Generate HTML documentation for all DOCS. By default, files are created in *PAX-WORLD-DIR* or (asdf:system-relative-pathname :mgl-pax "world/"), if NIL. DOCS is a list of entries of the form (NAME SECTIONS 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.

8 Markdown Support

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

8.1 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.

8.2 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.

8.3 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 Documentation Printer Variables

Docstrings are assumed to be in markdown format and they are pretty much copied verbatim to the documentation subject to a few knobs described below.


    When true, words with at least three characters and no lowercase characters naming an interned symbol are assumed to be code as if they were marked up with backticks which is especially useful when combined with *DOCUMENT-LINK-CODE*. For example, this docstring:

      "`FOO` and FOO."

    is equivalent to this:

      "`FOO` and `FOO`."

    iff FOO is an interned symbol. To suppress this behavior, add a backslash to the beginning of the symbol or right after the leading * if it would otherwise be parsed as markdown emphasis:


    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.


    If true, then the names of symbols recognized as code (including those found if *DOCUMENT-UPPERCASE-IS-CODE*) are downcased in the output if they only consist of uppercase characters. If it is :ONLY-IN-MARKUP, then if the output format does not support markup (e.g. it's :PLAIN), then no downcasing is performed.

  • [variable] *DOCUMENT-LINK-CODE* T

    When true, during the process of generating documentation for a SECTION, HTML anchors are added before the documentation of every reference that's not to a section. Also, markdown style reference links are added when a piece of inline code found in a docstring refers to a symbol that's referenced by one of the sections being documented. Assuming BAR is defined, the documentation for:

    (defsection @foo
      (foo function)
      (bar function))
    (defun foo (x)
      "Calls `BAR` on `X`."
      (bar x))

    would look like this:

      - [function] FOO X
          Calls [`BAR`][1] on `X`.

    Instead of BAR, one can write [bar][] or [`bar`][] as well. Since symbol names are parsed according to READTABLE-CASE, character case rarely matters.

    Now, if BAR has references with different locatives:

    (defsection @foo
      (foo function)
      (bar function)
      (bar type))
    (defun foo (x)
      "Calls `BAR` on `X`."
      (bar x))

    then documentation would link to all interpretations:

      - [function] FOO X
          Calls `BAR`([`1`][link-id-1] [`2`][link-id-2]) on `X`.

    This situation occurs in PAX with SECTION(0 1) which is both a class (see SECTION) and a locative type denoted by a symbol (see SECTION). Back in the example above, clearly, there is no reason to link to type BAR, so one may wish to select the function locative. There are two ways to do that. One is to specify the locative explicitly as the id of a reference link:

      "Calls [BAR][function] on X."

    However, if in the text there is a locative immediately before or after the symbol, then that locative is used to narrow down the range of possibilities. This is similar to what the M-. extension does. In a nutshell, if M-. works without questions then the documentation will contain a single link. So this also works without any markup:

      "Calls function `BAR` on X."

    This last option needs backticks around the locative if it's not a single symbol.

    Note that *DOCUMENT-LINK-CODE* can be combined with *DOCUMENT-UPPERCASE-IS-CODE* to have links generated for uppercase names with no quoting required.


    When true, HTML anchors are generated before the heading 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.


    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.


    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.


    If true, symbols are printed relative to SECTION-PACKAGE of the innermost containing section or with full package names if there is no containing section. To eliminate ambiguity [in package ...] messages are printed right after the section heading if necessary. If false, symbols are always printed relative to the current package.

10 Locative Types

These are the locatives type supported out of the box. As all locative types, they are symbols and their names should make it obvious what kind of things they refer to. Unless otherwise noted, locatives take no arguments.

  • [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] SECTION

    Refers to a section defined by DEFSECTION.


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


    Refers to a DEFCONSTANT. INITFORM, or if not specified, the value of the constant is included in the documentation.

  • [locative] MACRO

  • [locative] COMPILER-MACRO

  • [locative] FUNCTION

    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.

  • [locative] GENERIC-FUNCTION


    See CL:FIND-METHOD for the description of the arguments. To refer to the default method of the three argument generic function FOO:

      (foo (method () (t t t)))

  • [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.

  • [locative] CLASS

  • [locative] CONDITION

  • [locative] 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.")

    Note that while there is a CL:RESTART class, there is no corresponding source location or docstring like for CONDITIONs.

  • [locative] TYPE

    TYPE can refer to classes as well, but it's better style to use the more specific CLASS locative type for that. Another difference to CLASS is that an attempt is made at printing the arguments of type specifiers.

  • [locative] PACKAGE

  • [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 to (if *DOCUMENT-LINK-CODE*) its definition. However,


    will not be. On a dislocated locative LOCATE always fails with a LOCATE-ERROR condition.

  • [locative] ARGUMENT

    An alias for DISLOCATED, so the 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):

    "See the FORMAT in DOCUMENT."

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

    "See the FORMAT argument of DOCUMENT."


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


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

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


    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 "```commonlisp"
                            :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 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 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.

11 Extension API

11.1 Locatives and References

While Common Lisp has rather good introspective abilities, not everything is first class. For example, there is no object representing the variable defined with (DEFVAR FOO). (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 LOCATE-AND-COLLECT-REACHABLE-OBJECTS, LOCATE-AND-DOCUMENT and LOCATE-AND-FIND-SOURCE.

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


    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. If ERRORP, then a LOCATE-ERROR condition is signaled when the lookup fails.

  • [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.





    The first element of LOCATIVE if it's a list. If it's a symbol then it's that symbol itself. Typically, methods of generic functions working with locatives take locative type and locative args as separate arguments to allow methods have eql specializers on the type symbol.


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

11.2 Adding New Object Types

One may wish to make the DOCUMENT function and M-. navigation work with new object types. Extending DOCUMENT can be done by defining a DOCUMENT-OBJECT method. To allow these objects to be referenced from DEFSECTION, a LOCATE-OBJECT method is to be defined. Finally, for M-. FIND-SOURCE can be specialized. Finally, EXPORTABLE-LOCATIVE-TYPE-P may be overridden if exporting does not makes sense. Here is a stripped down example of 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 (symbol (locative-type (eql 'asdf:system))
  (assert (endp locative-args))
  ;; FIXME: This is slow as hell.
  (or (asdf:find-system symbol nil)

(defmethod canonical-reference ((system asdf:system))
  (make-reference (asdf::primary-system-name system) 'asdf:system))

(defmethod document-object ((system asdf:system) stream)
  (with-heading (stream system
                        (format nil "~A ASDF System Details"
                                (asdf::primary-system-name system)))
    (flet ((foo (name fn &key type)
             (let ((value (funcall fn system)))
               (when 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: ~A~%" name value)))))))
      (foo "Version" 'asdf/component:component-version)
      (foo "Description" 'asdf/system:system-description)
      (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 find-source ((system asdf:system))
    (:file ,(namestring (asdf/system:system-source-file system)))
    (:position 1)
    (:snippet "")))


    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.


    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 PACKAGE, ASDF:SYSTEM and METHOD return NIL.

    DEFSECTION calls this function to decide what symbols to export when its EXPORT argument is true.


    Return the object, to which OBJECT and the locative refer. For example, if LOCATIVE-TYPE is the symbol PACKAGE, this returns (FIND-PACKAGE SYMBOL). Signal a LOCATE-ERROR condition by calling the LOCATE-ERROR function if the lookup fails. Signal other errors if the types of the argument are bad, for instance LOCATIVE-ARGS is not the empty list in the package example. If a REFERENCE is returned then it must be canonical in the sense that calling CANONICAL-REFERENCE on it will return the same reference. For extension only, don't call this directly.


    Call this function to signal a LOCATE-ERROR condition from a LOCATE-OBJECT method. FORMAT-AND-ARGS contains a format string and args suitable for FORMAT from which the LOCATE-ERROR-MESSAGE is constructed. If FORMAT-AND-ARGS is NIL, then the message will be NIL too.

    The object and the locative are not specified, they are added by LOCATE when it resignals the condition.

  • [generic-function] CANONICAL-REFERENCE OBJECT

    Return a REFERENCE that resolves to OBJECT.


    Return a list of objects representing all things that would be documented in a (DOCUMENT OBJECT) call. For sections this is simply the union of references reachable from references in 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.


    This default implementation returns the empty list. This means that nothing is reachable from OBJECT.

  • [generic-function] DOCUMENT-OBJECT OBJECT STREAM

    Write OBJECT (and its references recursively) in FORMAT to STREAM.

    The DOCUMENT function calls this generic function with LEVEL 0, passing FORMAT on. Add methods specializing on OBJECT to customize how objects of that type are presented in the documentation.


    Print STRING verbatim to STREAM after cleaning up indentation.

    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.

  • [generic-function] FIND-SOURCE OBJECT

    Like SWANK:FIND-DEFINITION-FOR-THING, but this one is a generic function to be extensible. In fact, the default implementation simply defers to SWANK:FIND-DEFINITION-FOR-THING. This function is called by LOCATE-DEFINITION-FOR-EMACS which lies behind the M-. extension (see Emacs Integration).

    If successful, the return value looks like this:

    (:location (:file "/home/mega/own/mgl/pax/test/test.lisp")
               (:position 24) nil)

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

    (:error "Unknown source location for SOMETHING")

11.3 Reference Based Extensions

Let's see how to extend DOCUMENT and M-. navigation if there is no first class object to represent the thing of interest. Recall that LOCATE returns a REFERENCE object in this case. DOCUMENT-OBJECT and FIND-SOURCE defer to LOCATE-AND-DOCUMENT and LOCATE-AND-FIND-SOURCE, which have LOCATIVE-TYPE in their argument list for EQL specializing pleasure. Here is a stripped down example of 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.")

(defmethod locate-object (symbol (locative-type (eql 'variable)) locative-args)
  (assert (<= (length locative-args) 1))
  (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
    (locate-and-print-bullet locative-type locative-args symbol stream)
    (write-char #\Space stream)
    (multiple-value-bind (value unboundp) (symbol-global-value symbol)
      (print-arglist (prin1-to-string (cond (initformp initform)
                                            (unboundp "-unbound-")
                                            (t value)))
    (print-end-bullet stream)
    (with-dislocated-symbols ((list symbol))
      (maybe-print-docstring symbol locative-type stream))))

(defmethod locate-and-find-source (symbol (locative-type (eql 'variable))
  (declare (ignore locative-args))
  (find-one-location (swank-backend:find-definitions symbol)
                     '("variable" "defvar" "defparameter"


    Called by COLLECT-REACHABLE-OBJECTS on REFERENCE objects, this function has essentially the same purpose as its caller but it has different arguments to allow specializing on LOCATIVE-TYPE.


    This default implementation returns the empty list. This means that nothing is reachable from the reference.


    If REFERENCE can be resolved to a non-reference, call DOCUMENT-OBJECT with it, else call LOCATE-AND-DOCUMENT-OBJECT on the object, locative-type, locative-args of REFERENCE


    Called by DOCUMENT-OBJECT on REFERENCE objects, this function has essentially the same purpose as DOCUMENT-OBJECT but it has different arguments to allow specializing on LOCATIVE-TYPE.


    If REFERENCE can be resolved to a non-reference, call FIND-SOURCE with it, else call LOCATE-AND-FIND-SOURCE on the object, locative-type, locative-args of REFERENCE


    Called by FIND-SOURCE on REFERENCE objects, this function has essentially the same purpose as FIND-SOURCE but it has different arguments to allow specializing on LOCATIVE-TYPE.


    This default implementation simply calls FIND-SOURCE with OBJECT which should cover the common case of a macro expanding to, for instance, a defun but having its own locative type.

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.

11.4 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.


    *PACKAGE* will be bound to this package when generating documentation for this section.


    *READTABLE* will be bound to this when generating documentation for this section.


    STRING or NIL. Used in generated documentation.


    A REFERENCE or NIL. Used in generated documentation.


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

12 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. The 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 and its 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)

12.1 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:*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 adding this to your Emacs initialization file (or loading src/transcribe.el):

;;; MGL-PAX transcription

(defun mgl-pax-transcribe-last-expression ()
  "A bit like C-u C-x C-e (slime-eval-last-expression) that
inserts the output and values of the sexp before the point, this
does the same but with MGL-PAX:TRANSCRIBE. Use a numeric prefix
argument as in index to select one of the Common Lisp
Without a prefix argument, the first syntax is used."
     (let* ((end (point))
            (start (progn (backward-sexp)
                          (move-beginning-of-line nil)
       (mgl-pax-transcribe start end (mgl-pax-transcribe-syntax-arg)
                           nil nil nil)))))

(defun mgl-pax-retranscribe-region (start end)
  "Updates the transcription in the current region (as in calling
MGL-PAX:TRANSCRIBE with :UPDATE-ONLY T). Use a numeric prefix
argument as in index to select one of the Common Lisp
Without a prefix argument, the syntax of the input will not be
  (interactive "r")
  (let* ((point-at-start-p (= (point) start))
         (point-at-end-p (= (point) end))
         (transcript (mgl-pax-transcribe start end
                                         t t nil)))
    (if point-at-start-p
          (goto-char start)
          (delete-region start end)
          (insert transcript))
          (goto-char start)
          (delete-region start end))
      (insert transcript))))

(defun mgl-pax-transcribe-syntax-arg ()
  (if current-prefix-arg
      (prefix-numeric-value current-prefix-arg)

(defun mgl-pax-transcribe (start end syntax update-only echo
  (let ((transcription
          `(cl:if (cl:find-package :mgl-pax)
                    (cl:symbol-name :transcribe-for-emacs) :mgl-pax)
                   ,(buffer-substring-no-properties start end)
                   ',syntax ',update-only ',echo ',first-line-special-p)
    (if (eq transcription t)
        (error "MGL-PAX is not loaded.")

12.2 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, 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)
    => (1

    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=. 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. There is currently no remedy for that, except for customizing PRINT-OBJECT or not transcribing that kind of stuff.


    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.

  • [variable] *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 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.

[generated by MGL-PAX]


Exploratory programming environment and documentation generator.




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