You can use the functions from macro-debugger/expand to do this (within
limits). Here's a very rough example program that reads one term from
stdin and shows its expansion with the given hiding policy (discarding
hygiene information---beware).
usage: racket expand.rkt < your-example-file.rkt
Ryan
On 8/10/20 3:44 PM, Éric Tanter wrote:
Hi,
I’d like to use the Racket macro expander to translate programs from a
given source language to a target language (both scheme-ish).
However, the expansion that `raco expand` does is too violent for my
purposes---I would need a way to specify macro hiding (as in the macro
stepper), in order to control the level of abstraction of the expanded
code. Is that possible?
[see example below]
Thanks,
— Éric
; test.rkt
(define-syntax-rule (swap x y)
(let ([tmp x])
(set! x y)
(set! y tmp)))
(define a 10)
(define b 20)
(swap a b)
; I’d like to obtain:
…prelude…
(define a 10)
(define b 20)
(let ([tmp a])
(set! a b)
(set! b tmp)))
; but raco expand gives me the full story:
(module test play
(#%module-begin
(module configure-runtime '#%kernel
(#%module-begin (#%require racket/runtime-config) (#%app configure
'#f)))
(#%provide b swap a)
(define-syntaxes
(swap)
(lambda (user-stx)
(let-values (((arg) user-stx))
(let-values (((rslt)
(#%app
(lambda (e)
(if (#%app stx-pair? e)
(if (#%app (lambda (e) null) (#%app stx-car e))
(#%app
(lambda (e)
(if (#%app stx-pair? e)
(#%app
cons/#f
(#%app stx-car e)
(#%app
(lambda (e)
(if (#%app stx-pair? e)
(let-values (((mh) (#%app
stx-car e)))
(if mh
(if (#%app
stx-null/#f
(#%app stx-cdr e))
mh
'#f)
'#f))
'#f))
(#%app stx-cdr e)))
'#f))
(#%app stx-cdr e))
'#f)
'#f))
arg)))
(if rslt
(let-values (((sc1) (#%app unsafe-car rslt))
((sc2) (#%app unsafe-cdr rslt)))
(let-values ()
(#%app
syntax-protect
(let-values (((loc) (#%app check-loc 'syntax/loc
user-stx)))
(#%app
t-subst
loc
(quote-syntax (let _ (set! _ _) (set! _ tmp)))
'(1 recur 2 recur 3)
(#%app
t-resyntax
'#f
(quote-syntax STX)
(#%app
t-list
(#%app t-subst '#f (quote-syntax (tmp _)) '(1) sc1)))
(#%app list '(1 2) sc1 sc2)
(#%app list '(1) sc2))))))
(let-values (((rslt) (#%app (lambda (e) null) arg)))
(if rslt
(let-values ()
(let-values () (#%app pattern-failure user-stx '(x y))))
(#%app raise-syntax-error '#f '"bad syntax" arg))))))))
(define-values (a) '10)
(define-values (b) '20)
(#%app
call-with-values
(lambda () (let-values (((tmp) a)) (set! a b) (set! b tmp)))
print-values)))
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#lang racket/base
(require syntax/modread
macro-debugger/expand
racket/pretty)
;; Read a term from stdin, expand, and show expansion (but only of
;; selected identifiers).
(define stx (with-module-reading-parameterization
(lambda () (read-syntax #f (current-input-port)))))
;; Replace this with the predicate you care about...
(define (show-macro? id)
(memq (syntax-e id) '(swap)))
(define-namespace-anchor a)
(define ns (namespace-anchor->namespace a))
(pretty-print
(syntax->datum
(parameterize ((current-namespace ns))
(expand/show-predicate stx show-macro?))))
