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clean up `set!' implementation in ASL to avoid catching failures

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The code seems to pre-date the failure thunk to `syntax-local-value'.
A problem with letting an exception get raised is that it triggers
the `error-value->string' handler, which loads Slideshow pict support
in DrRacket, which loads `racket/draw' at phase 1 --- which isn't
inherenty bad, but a lot of work that can be avoided.
This commit is contained in:
Matthew Flatt 2011-12-02 16:02:11 -07:00
parent 745c4b6470
commit 7ddbc95b51
1 changed files with 22 additions and 20 deletions
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42
collects/lang/private/teach.rkt
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@ -2344,26 +2344,28 @@
(identifier? (syntax id))
(let ([exprs (syntax->list (syntax (expr ...)))])
;; Check that id isn't syntax, and not lexical.
(when ((with-handlers ([exn:fail? (lambda (exn) (lambda () #t))])
;; First try syntax:
(let ([binding (syntax-local-value (syntax id))])
;; If it's a transformer binding, then it can take care of itself...
(if (set!-transformer? binding)
(lambda () #f) ;; no lex check wanted
(lambda ()
(teach-syntax-error
'set!
stx
(syntax id)
"expected a variable after set!, but found a ~a" (syntax-e #'id)))))))
;; Now try lexical:
(when (eq? 'lexical (identifier-binding (syntax id)))
(teach-syntax-error
'set!
stx
(syntax id)
"expected a mutable variable after set!, but found a variable that cannot be modified: ~a"
(syntax-e #'id))))
;; First try syntax:
(let ([binding (syntax-local-value (syntax id) (lambda () #f))])
;; If it's a transformer binding, then it can take care of itself...
(cond
[(set!-transformer? binding)
;; no lex check wanted
(void)]
[(not binding)
;; Now try lexical:
(when (eq? 'lexical (identifier-binding (syntax id)))
(teach-syntax-error
'set!
stx
(syntax id)
"expected a mutable variable after set!, but found a variable that cannot be modified: ~a"
(syntax-e #'id)))]
[else
(teach-syntax-error
'set!
stx
(syntax id)
"expected a variable after set!, but found a ~a" (syntax-e #'id))]))
;; If we're in a module, we'd like to check here whether
;; the identier is bound, but we need to delay that check
;; in case the id is defined later in the module. So only