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Article contents:== Outdated egg! This is an egg for CHICKEN 3, the unsupported old release. You're almost certainly looking for [[/eggref/4/codewalk|the CHICKEN 4 version of this egg]], if it exists. If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-4.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN. [[tags:eggs]] [[toc:]] == codewalk A generic macro-expansion and code-walking and code-transformation facility. === expand [procedure] (expand EXPRESSION [HOOK [ARGUMENT ...]]) Recursively expands macros in {{EXPRESSION}}, calling the procedure {{HOOK}} (if provided). The hook is called with 5 or more arguments: (HOOK EXPR CLASS WALK ENV MARK ARGUMENT ...) {{EXPR}} is the currently traversed subexpression, {{CLASS}} is a symbol identifying the expression class, {{WALK}} is a procedure of one or more arguments that should be called to walk sub-expressions of {{EXPR}} recursively. The additional arguments {{ARGUMENT ...}} will be passed to the hook as additional parameters, which in turn should pass the same number of extra arguments to recursive invocations of {{WALK}} (plus the sub-expression to walk). {{ENV}} is a list of lists containing the lexical environment, where each list is a list of lexically bound identifiers (symbols). The frontmost list holds the current environment. {{MARK}} is a procedure of one argument that can be used to mark subexpressions which should not be traversed by {{HOOK}}. Invoking {{WALK}} with the same ({{eq?}}) {{EXPR}} that has been given as the first argument to {{HOOK}} performs default processing and walking of subexpressions of {{EXPR}}. Note that the default processing returns S-expressions. If you want to use {{expand}} to create some other type (for example an abstract syntax tree of dedicated node records), you have to provide treatment and translation for all expression classes. === expand/context [procedure] (expand/context EXPRESSION CONTEXT [HOOK [ARGUMENT ...]]) Similar to {{expand}}, but allows passing additional expansion-parameters, which should be created by calling {{expansion-context}}. === expansion-context [procedure] (expansion-context #!key evaluate compilation unsafe cooked classes prehook environment) Creates an ''expansion-context'' that is used to pass additional expansion parameters to {{expand/context}}. The keyword arguments have the following meaning: ; evaluate : should macro-expansion time evaluation be performed (for example, in an {{eval-when}} clause) (boolean, default: {{#f}}). ; compilation : does the expansion happen during compilation (as opposed to interpretation) (boolean, default: {{#t}} when called during compilation or {{#f}} otherwise). ; unsafe : does the expansion happen in an unsafe compilation context (boolean, default: {{#f}}). ; classes : list of symbols identifying the classes of expressions for which the hook should be called during expansion (list or {{#t}}, default: {{#t}}). ; cooked : whether internal forms that perform expansion-time evaluation or other special processing (usually compiler-specific) be processed as they appear ({{#t}}) or whether they should be passed through to the hook function - passing {{#t}} for {{evaluate}} implies cooked mode. ; prehook : a procedure accepting at least 3 arguments, an expression, an environment and a continuation. This procedure will be called before any macroexpansion with the to-be-expanded expression in the first argument position. The continuation argument should be called with the actual expression to be expanded (or the original one) and any additional arguments. Returning from the prehook procedure without calling the continuation is undefined. ; environment : the initial environment used in the expansion. The following expression classes exist: ; ref : variable reference ; literal : literal constant ; quoted-literal : quoted literal constant ; undefined : an undefined value - note that this means really ''undefined'', not {{(void)}} ; if : {{if}} conditional ; begin : {{begin}} sequence ; set! : assignment ; let : {{let}} binding form ; lambda : {{lambda}} expression ; app : procedure application ; compiler-form : compiler special form ; require : {{require-extension}} or {{require-for-syntax}} form (or internal equivalent) ; special : special internal form - should normally be treated as a call to an identity function Note that external macro packages like [[http://code.call-cc.org/legacy-eggs/3/syntax-case.html|syntax-case]] expand their input completely, so the {{prehook}} will already get macroexpanded forms. === expansion-context? [procedure] (expansion-context? X) Returns {{#t}} if {{X}} is an expansion context, or {{#f}} otherwise. === install-toplevel-expander [procedure] (install-toplevel-expander EXPANDER [OVERRIDE-MACROEXPAND]) Installs {{EXPANDER}} as the ''toplevel'' macro expander for subsequent interpretation or compilation. If {{OVERRIDE-MACROEXPAND}} is given and true, then {{macroexpand}} will also invoke the given expander and no further internal macroexpansion takes place. Use this when you want to install a custom macroexpansion package that does complete processing of syntax transformation. If you merely want to do some custom pre-processing, pass {{#f}} for this argument (or omit it completely). === Examples (define exp '(begin (define (count-bits2 n result) (if (zero? n) result (count-bits2 (bitwise-and n (sub1 n)) (add1 result)))) (time (do ((i 0 (add1 i))) ((>= i 10)) (print (count-bits2 i 0))))) ) (pp (expand exp)) ; expand all macros (define exp2 ; trace global variable references (expand exp (lambda (x c w e m) (if (and (symbol? x) (not (ormap (cut memq x <>) e))) (w (m `(let ((x ,x)) (print "ref: " ',x " = " x) x) ) ) (w x) ) ) ) ) (pp exp2) (pp (eval exp2)) ; the code can be evaluated as usual (define exp3 ; trace all calls (expand/context exp (expansion-context classes: '(app)) (lambda (x c w e m) (let ((fn (gensym))) (w (m `((let ((,fn ,(car x))) (print "calling: " ,fn) ,fn) ,@(map w (cdr x) ) ) ) ) ) ) ) ) (pp exp3) (pp (eval exp3)) (define (instrument-calls exp pred? mod) ;; instrument calls that satisfy a given predicate (expand/context exp (expansion-context classes: '(app)) (lambda (x c w e m) (if (pred? x) (w (m (mod (map w x)))) (w x) ) ) ) ) (define exp4 ; trace calls (instrument-calls exp (constantly #t) (lambda (call) (let ((v (gensym))) `(begin (print "calling: " ',call) ,call) ) ) ) ) (pp exp4) (eval exp4) ;;;; count direct calls to "car" (use miscmacros) (define n 0) (define (count exp) (expand/context exp (expansion-context classes: '(app)) (lambda (x c w e m) (match x (('car arg) (inc! n) `(car ,(w arg)) ) (_ (w x)) ) ) ) ) (for-each count (read-file "codewalk.scm")) (pp n) ; should be "7" == Authors [[/users/felix winkelmann|felix winkelmann]] == License Copyright (c) 2006-2007, Felix L. Winkelmann All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. Neither the name of the author nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. == Version History ; 0.4 : certain internal lambda-forms didn't get properly expanded [Thanks to Benedikt Rosenau for reporting this] ; 0.3 : doesn't use interpreter-specific expansion hook anymore (doesn't work with syntax-case, otherwise) ; 0.2 : minor bugfixes, added support for "prehook" and "environment" context args ; 0.1 : initial release Description of your changes:

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