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From misc/syntax-case.scm:

; Note that Gambit's normal parser processes the ; input after expansion by the syntax-case expander. Since the ; syntax-case expander does not know about Gambit's syntactic ; extensions (like DSSSL parameters) some of the syntactic ; extensions cannot be used.

One of those Gambit extensions is define-structure. So the portable syntax-case expander thinks that

(define-structure ...)

is a function call, so it thinks the "define" that follows it is illegal.

I think this should work:

(define-only (mkcounter inc! val) (define-structure counter v) ;; Invisible from the top-level. (let () (define mkcounter (lambda () (make-counter 0))) (define inc! (lambda (c) (counter-v-set! c (+ 1 (counter-v c))))) (define val counter-v) #f))

Also, you can get around this problem by using your own definition for define-structure, for example this one from misc/psyntax73.scm:

(define-syntax define-structure (lambda (x) (define construct-name (lambda (template-identifier . args) (datum->syntax-object template-identifier (string->symbol (apply string-append (map (lambda (x) (if (string? x) x (symbol->string (syntax-object->datum x)))) args)))))) (syntax-case x () ((_ (name id1 ...)) (andmap identifier? (syntax (name id1 ...))) (with-syntax ((constructor (construct-name (syntax name) "make-" (syntax name))) (predicate (construct-name (syntax name) (syntax name) "?")) ((access ...) (map (lambda (x) (construct-name x (syntax name) "-" x)) (syntax (id1 ...)))) ((assign ...) (map (lambda (x) (construct-name x "set-" (syntax name) "-" x "!")) (syntax (id1 ...)))) (structure-length (+ (length (syntax (id1 ...))) 1)) ((index ...) (let f ((i 1) (ids (syntax (id1 ...)))) (if (null? ids) '() (cons i (f (+ i 1) (cdr ids))))))) (syntax (begin (define constructor (lambda (id1 ...) (vector 'name id1 ... ))) (define predicate (lambda (x) (and (vector? x) (= (vector-length x) structure-length) (eq? (vector-ref x 0) 'name)))) (define access (lambda (x) (vector-ref x index))) ... (define assign (lambda (x update) (vector-set! x index update))) ...)))))))

Marc

On 16-Apr-07, at 1:20 PM, TJ wrote:

I have a macro defined thus:

(define-syntax define-only (lambda (exp) (syntax-case exp () ((_ (n ...) e ...) (with-syntax (((tmp ...) (generate-temporaries (syntax (n ...))))) (syntax (begin (define n #f) ... (let ((tmp #f) ...) ((lambda () e ... (set! tmp n) ...)) (set! n tmp) ...))))))))

Which, if it works, would enable me to do the following:

(define-only (mkcounter inc! val) (define-structure counter v) ;; Invisible from the top-level. (define mkcounter (lambda () (make-counter 0))) (define inc! (lambda (c) (counter-v-set! c (+ 1 (counter-v c))))) (define val counter-v))

But which, unfortunately, gives me the following:

*** ERROR -- invalid context for definition (define mkcounter (lambda () (make-counter 0)))

I suspected that perhaps (define...)'s were not allowed after (define-structure...)'s. So I did this:

(pp (lambda () (define-structure test a) 'done))

Which prints the following:

(lambda () (letrec ((##type-1-test (##structure ##type-type (##make-uninterned-symbol "##type-1-test") 'test 8 #f '#(a 0 #f))) (make-test (lambda (p1) (##structure ##type-1-test p1))) (test? (lambda (obj) (##structure-direct-instance-of? obj (##type-id ##type-1-test)))) (test-a (lambda (obj) (##direct-structure-ref obj 1 ##type-1-test test-a))) (test-a-set! (lambda (obj val) (##direct-structure-set! obj val 1 ##type-1-test test-a-set!)))) 'done))

Which makes me wonder why my macro doesn't work. After all (define...)'s are allowed at the beginning of a letrec's body, no?

TJ _______________________________________________ Gambit-list mailing list Gambit-list@iro.umontreal.ca https://webmail.iro.umontreal.ca/mailman/listinfo/gambit-list