Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Codewalk the form and find, which variables and functions are undefined.
Common Lisp

Fetching latest commit…

Cannot retrieve the latest commit at this time

Failed to load latest commit information.
COPYING
README.md
cl-indeterminism.asd
cl-indeterminism.lisp
package.lisp
tests.lisp

README.md

cl-indeterminism

Do some cool stuff with undefined functions and variables.

By now, 'cool stuff' includes:

  • FIND-UNDEFS - described in section "Finding"
  • MACROEXPAND-ALL-TRANSFORMING-UNDEFS - described in section "Transforming"
  • MACROEXPAND-CC-ALL-TRANSFORMING-UNDEFS - described in section "Transforming at compile-time"

Finding

Codewalk the form and find, which variables and functions are undefined.

CL-USER> (ql:quickload 'cl-indeterminism)
CL-USER> (cl-indeterminism:find-undefs '(foo bar baz))
((:FUNCTIONS FOO) (:VARIABLES BAZ BAR))

FIND-UNDEFS is now a macro which expands in the surrounding context, making it possible to catch undefined variables relative to the current lexenv.

CL-USER> (let ((a 1)) (cl-indeterminism:find-undefs 'a))
((:FUNCTIONS) (:VARIABLES))

Still, one can explicitly specify to find undefs with respect to top-level environment

CL-USER> (let ((a 1)) (cl-indeterminism:find-undefs 'a :env :null))
((:FUNCTIONS) (:VARIABLES A))

Can be also used to find list of undefined variables at compile time

(defmacro list-the-undefs (&body body &environment env)
  `(list ,@(mapcar (lambda (x) `(quote ,x))
           (find-undefs `(progn ,@body) :env env))))
(let ((bar 1)) (declare (ignore bar)) (find-undefs '(foo bar baz)))
((:FUNCTIONS FOO) (:VARIABLES BAZ))

Uses profound HU.DWIM.WALKER system to do the heavy lifting of code walking and is, in fact, just a convenience wrapper around it.

Note: if your implementation is not supported by HU.DWIM.WALKER or CL-CURLEX, then branch "without-curlex" is for you - there initial unsophisticated behaviour of the system is fixed forever.

Transforming

Codewalk the form and transform undefined variables and functions in it on the fly to something else. Has a side effect of expanding all the macros in the form.

CL-USER> (ql:quickload 'cl-indeterminism)
CL-USER> (let ((cl-indeterminism:*variable-transformer* (lambda (x) `(quote ,x))))
           (cl-indeterminism:macroexpand-all-transforming-undefs '(a b c)))
(A 'B 'C)
CL-USER> (let ((cl-indeterminism:*function-transformer*
                (lambda (form)
                  (if (keywordp (car form))
                      (cl-indeterminism:fail-transform)
                      `(,(intern (string (car form)) "KEYWORD")
                        ,@(cdr form))))))
           (cl-indeterminism:macroexpand-all-transforming-undefs '(a b c)))
(:A B C)

The API consists of the following ingredients:

  • MACROEXPAND-ALL-TRANSFORMING-UNDEFS - macro, which actually does the transformation. Accepts optional keyword :ENV, which can be :NULL or :CURRENT (default) and acts the same as in FIND-UNDEFS.
  • *VARIABLE-TRANSFORMER* - NIL, or a reference to a function, which accepts variable name, and returns arbitrary lisp-form. This function is used to transform all undefined variables. If NIL, variables are left as-is, nothing happens. If non-NIL, the returned form is recursively walked, so all undefined variables and function in it are also expanded. Beware of infinite recursions, use FAIL-TRANSFORM to prevent it!
  • *FUNCTION-TRANSFORMER* - analogous to *VARIABLE-TRANSFORMER*, only handles transformation of undefined functions. When NIL, undefined functions are left as-is. When non-NIL, expected to accept entire form on undefined function call and return arbitrary lisp-form. The returned form is recursively walked, so all undefined variables and function in it are also expanded. Beware of infinite recursions, use FAIL-TRANSFORM to prevent it!
  • FAIL-TRANSFORM - a macro, which can be used inside functions, to which *VARIABLE-TRANSFORMER* and *FUNCTION-TRANSFORMER* are bound. When invoked, causes transformation not to be performed, that is undefined variable/function call is left as-is. Useful to prevent infinite recursions, as in example above, when transformation on unknown function is not performed if its name is already a keyword.

I personally plan to use all this machinery in my fork of ESRAP packrat parser (https://github.com/mabragor/esrap). There, the idea is to transform all undefined variable names inside DEFRULE macro into calls to functions, which try to continue parsing with help of a rule, corresponding to the name of undefined variable. See branch 'liquid' there for examples of usage of MACROEXPAND-ALL-TRANSFORMING-UNDEFS.

Transforming at compile-time

Works similar to transforming at runtime, but is far more interesting, isn't it?

CL-USER> (ql:quickload 'cl-indeterminism)
CL-USER> (defmacro autoquote (form &environment env)
           (let ((cl-indeterminism:*variable-transformer* (lambda (x) `(quote ,x))))
             (cl-indeterminism:macroexpand-cc-all-transforming-undefs form :env env)))
;; So, our AUTOQUOTE macro automatically quotes
;; all the undefined variables inside its form
CL-USER> (defun foo ()
           (autoquote (list b c)))
CL-USER> (foo)
(B C)
;; And it takes into account lexical environment
;; it is expanded in, so here B is not quoted
CL-USER> (let ((b 1))
           (defun foo ()
             (autoquote (list b c))))
CL-USER> (foo)
(1 C)

Note, that lexical environment has to be explicitly fetched with help of &ENVIRONMENT keyword of the enclosing macro and passed to MACROEXPAND-CC-ALL-TRANSFORMING-UNDEFS. This is due to my failure to fetch this compile environment in some implementations with some other tricks.

TODO:

  • (done) find undefined variables with respect to current lexenv, not null lexenv
    • (done) allow to specify null lexenv
  • (done) macro to manipulate undefined functions and variables conveniently

BUGS & GOTCHAS:

  • MACROLETs in the enclosing scope are not handled correctly

    CL-USER> (macrolet ((bar (b) nil)) (cl-indeterminism:find-undefs '(bar a)))
    ((:FUNCTIONS) (:VARIABLES A))
    

    although it should see that variable A is not really there (hence, it does not go into the body of BAR). This is due to the limitation of CL-CURLEX, where only names of functions, variabes and macros are captured, not their definitions.

  • HU.DWIM.WALKER, which is used in implementation of MACROEXPAND-ALL-TRANSFORMING-UNDEFS and MACROEXPAND-CC-ALL-TRANSFORMING-UNDEFS does not know about some declarations, specific to compilers, such as TRULY-DYNAMIC-EXTENT. This results in tons of style warnings on standard output. So, for now I simply kludged to muffle those. However, if you suspect that macroexpansion is done wrong, you maybe should enable those warnings again, look for clues, and then maybe send a patch :)
Something went wrong with that request. Please try again.