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allow definition in module to shadow a preceding import

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This change is experimental and intended to reduce (but certainly not
eliminate) the problem of breaking existing code by adding exports to
a module.
This commit is contained in:
Matthew Flatt 2015-06-23 20:48:47 +08:00
parent fae92a19f5
commit ea016bec96
3 changed files with 22 additions and 11 deletions
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11
pkgs/racket-doc/scribblings/reference/syntax.scrbl
View File

@ -224,7 +224,10 @@ declarations for @racket[A] and @racket[B]. However, a syntactic form
that produces syntax definitions must be defined before it is used.
No identifier can be imported or defined more than once at any
@tech{phase level} within a single module. Every exported identifier must be imported or
@tech{phase level} within a single module, except that a definition
via @racket[define-values] or @racket[define-syntaxes] can shadow a
preceding import via @racket[#%require].
Every exported identifier must be imported or
defined. No expression can refer to a @tech{top-level variable}.
A @racket[module*] form in which the enclosing module's bindings are visible
(i.e., a nested @racket[module*] with @racket[#f] instead of a @racket[module-path])
@ -300,7 +303,11 @@ See also @secref["module-eval-model"] and @secref["mod-parse"].
(unless (zero? n)
(printf "quack\n")
(quack (sub1 n)))))
]}
]
@history[#:changed "6.2.0.4" @elem{Changed @racket[define-syntaxes]
and @racket[define-values] to
shadow any preceding import.}]}
@defform*[((module* id module-path form ...)

10
pkgs/racket-test-core/tests/racket/module.rktl
View File

@ -127,7 +127,6 @@
(syntax-test #'(module m racket/base (#%require (rename n n not-there))))
(syntax-test #'(module m racket/base (#%require (rename n n m extra))))
(syntax-test #'(module m racket/base (#%require racket/base) (define car 5)))
(syntax-test #'(module m racket/base (define x 6) (define x 5)))
(syntax-test #'(module m racket/base (define x 10) (define-syntax x 10)))
(syntax-test #'(module m racket/base (define-syntax x 10) (define x 10)))
@ -142,6 +141,15 @@
(test 5 dynamic-require ''_shadow_ 'car)
;; Ok to redefine imported:
(module defines-car-that-overrides-import racket/base (#%require racket/base) (define car 5) (provide car))
(module defines-car-that-overrides-import/stx racket/base (#%require racket/base (for-syntax racket/base)) (define-syntax (car stx) #'6) (provide car))
(test 5 dynamic-require ''defines-car-that-overrides-import 'car)
(test 6 dynamic-require ''defines-car-that-overrides-import/stx 'car)
;; Can't redefine multiple times or import after definition:
(syntax-test #'(module m racket/base (#%require racket/base) (define car 5) (define car 5)))
(syntax-test #'(module m racket/base (define car 5) (#%require racket/base)))
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(let ()

12
racket/src/racket/src/module.c
View File

@ -8959,11 +8959,9 @@ static Scheme_Object *do_module_begin_at_phase(Scheme_Object *form, Scheme_Comp_
return NULL;
}
/* Not required: */
if (check_already_required(required, name)) {
scheme_wrong_syntax(who, orig_name, e, "identifier is already imported");
return NULL;
}
if (check_already_required(required, name)) {
/* allow definition of previously imported */
}
/* Not syntax: */
if (scheme_lookup_in_table(env->genv->syntax, (const char *)name)) {
@ -9062,10 +9060,8 @@ static Scheme_Object *do_module_begin_at_phase(Scheme_Object *form, Scheme_Comp_
return NULL;
}
/* Not required: */
if (check_already_required(required, name)) {
scheme_wrong_syntax(who, orig_name, e, "identifier is already imported");
return NULL;
/* allow definition of previously imported */
}
if (!SAME_OBJ(SCHEME_STX_VAL(orig_name), name)) {