fwiw, I think here is a working version along the lines of your
original attempt.
#lang racket
(require (for-syntax syntax/parse))
(define-syntax set/define
(syntax-parser
[(_ h k v)
#:when (with-handlers ([exn:fail:syntax:unbound? (lambda _ #f)])
(local-expand #'h 'expression null))
#'(hash-set! h 'k v)]
[(_ h k v)
#'(begin
(define h (make-hash))
(hash-set! h 'k v))]))
(set/define h a 1)
(set/define h a 2)
(hash-set! h 'b 42)
h ; '#hash((b . 42) (a . 2))
(define bar (make-hash))
(set/define bar a 1)
bar ; '#hash((a . 1))
(define (foo)
(set/define local-h a 1)
(set/define local-h a 2)
(hash-set! local-h 'b 42)
local-h)
(foo) ; '#hash((b . 42) (a . 2))
On Sat, Apr 20, 2019 at 6:24 PM Shu-Hung You
<shu-hung....@eecs.northwestern.edu> wrote:
>
> identifier-binding returns #f for top-level bindings. I believe
> make-base-eval is evaluating expressions at top-level.
>
> On Sat, Apr 20, 2019 at 4:56 PM Ryan Kramer <default.kra...@gmail.com> wrote:
> >
> > Below is a short example showing that identifier-binding doesn't seem to
> > work quite right with Scribble's make-base-eval. It works fine with
> > make-evaluator from racket/sandbox.
> >
> > I'm not sure why this is, but using syntax-local-value instead works
> > everywhere. (Implementation here:
> > https://github.com/default-kramer/plisqin/commit/2723d7c11be5b6938e681ea869e8b9f4957849b0#diff-1a91d998f2be05413392d588a89323d3R31)
> >
> > #lang racket
> > (require scribble/eval
> > racket/sandbox)
> >
> > (define (setup eval)
> > (eval
> > '(define-syntax (define-if-not stx)
> > (syntax-case stx ()
> > [(_ id val)
> > (identifier-binding #'id)
> > #'(void)]
> > [(_ id val)
> > #'(define id val)]))))
> >
> > (define scribble-eval (make-base-eval))
> > (scribble-eval '(require racket))
> > (setup scribble-eval)
> >
> > (define racket-eval (make-evaluator 'racket))
> > (setup racket-eval)
> >
> > (scribble-eval '(define-if-not foo 1))
> > (scribble-eval '(define-if-not foo 2))
> > (scribble-eval 'foo) ; want 1, get 2
> >
> > (racket-eval '(define-if-not bar 3))
> > (racket-eval '(define-if-not bar 4))
> > (racket-eval 'bar) ; want 3, get 3
> >
> > --
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