I am trying to get a macro to expand at compile time using eval-when, but it’s not giving me what I expect:
(eval-when (expand) (make-regexp pat)) …
gets expanded to:
(if #f #f)
I would like to see something like
#<regexp 1098a2d40>
Any help would be appreciated. — Matt
I get the same (if #f #f) result whether I use (expand) or (compile).
Below is 1) my macro (missing the helpers all-const-string? and rx-let)
2) the macro I use to compile to il-tree and then back to scheme
3) the demo code
4) the output from expand
=== my macro ==========================
(define-syntax regexp-case
(lambda (x)
(syntax-case x (else)
((_ str ((pat v ...) exp ...) ... (else else-exp ...))
(with-syntax (((id ...) (generate-temporaries #'(pat ...))))
(all-const-string? #'(pat ...))
#'(let ((id (eval-when (expand) (make-regexp pat))) ...)
(cond
((regexp-exec id str) =>
(lambda (m) (rx-let m (v ...) exp ...)))
...
(else else-exp ...)))))
((_ str ((pat v ...) exp ...) ...)
(with-syntax (((id ...) (generate-temporaries #'(pat ...))))
(all-const-string? #'(pat ...))
#'(let ((id (eval-when (expand) (make-regexp pat))) ...)
(cond
((regexp-exec id str) =>
(lambda (m) (rx-let m (v ...) exp ...)))
...
(else
(scm-error #f "regexp-case"
"no match found: ~S" (list str)
#f)))))))))
=== the expand macro =======================
#:use-module (srfi srfi-11)
#:use-module (system base compile)
(define* (expand-form e #:key (opts '()))
(let-values (((exp env) (decompile
(compile e #:from 'scheme
#:to 'tree-il
#:env (current-module))
#:from 'tree-il
#:to 'scheme
#:opts opts)))
exp))
(define-syntax-rule (expand _expression_)
(expand-form '_expression_))
=== orig test case ================
(regexp-case str
(("^([a-z]+)\\(([0-9]+)\\)$" v i)
(list v i))
(("^([a-z]+)$" v)
(list v "1")))
=== output from expand =============
(let ((t-768 (if #f #f))
(t-769 (if #f #f)))
(let ((t (regexp-exec t-768 str)))
(if t
(let ((m t))
(let ((v (match:substring m 1))
(i (match:substring m 2)))
(list v i)))
(let ((t (regexp-exec t-769 str)))
(if t
(let* ((m t) (v (match:substring m 1)))
(list v "1"))
(scm-error
#f
"regexp-case"
"no match found: ~S"
(list str)
#f))))))