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doc clarifications on module constants

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svn: r13248
This commit is contained in:
Matthew Flatt 2009-01-21 15:44:30 +00:00
parent 2e35104f84
commit ea0958e362
2 changed files with 19 additions and 7 deletions
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15
collects/scribblings/guide/module-set.scrbl
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@ -45,14 +45,19 @@ binding. For essentially the same reason that it helps programmers,
the prohibition on assignment to imports also allows many programs to the prohibition on assignment to imports also allows many programs to
be executed more efficiently. be executed more efficiently.
Along the same lines, re-declaration of a module is not generally Along the same lines, when a module contains no @scheme[set!] of a
allowed. Indeed, for file-based modules, simply changing the file does particular identifier that is defined within the module, then the
not lead to a re-declaration, because file-based modules are loaded on identifier is considered a @defterm{constant} that cannot be
changed---not even by re-declaring the module.
Consequently, re-declaration of a module is not generally allowed.
For file-based modules, simply changing the file does not lead to a
re-declaration in any case, because file-based modules are loaded on
demand, and the previously loaded declarations satisfy future demand, and the previously loaded declarations satisfy future
requests. It is possible to use Scheme's reflection support to requests. It is possible to use Scheme's reflection support to
re-declare a module, however, and non-file modules can be re-declared re-declare a module, however, and non-file modules can be re-declared
in the @tech{REPL}; in such cases, the redeclaration may fail if it in the @tech{REPL}; in such cases, the re-declaration may fail if it
involves the re-definition of a previously immutable binding. involves the re-definition of a previously constant binding.
@interaction[ @interaction[
(module m scheme (module m scheme

11
collects/scribblings/reference/syntax.scrbl
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@ -164,7 +164,7 @@ defined. No expression can refer to a @tech{top-level variable}.
The evaluation of a @scheme[module] form does not evaluate the The evaluation of a @scheme[module] form does not evaluate the
expressions in the body of the module. Evaluation merely declares a expressions in the body of the module. Evaluation merely declares a
module, whose full name depends both on @scheme[id] and module, whose full name depends both on @scheme[id] and
@scheme[(current-module-name-prefix)]. @scheme[(current-module-declare-name)].
The module body is executed only when the module is explicitly The module body is executed only when the module is explicitly
@techlink{instantiate}d via @scheme[require] or @techlink{instantiate}d via @scheme[require] or
@ -173,7 +173,12 @@ are evaluated in order as they appear within the module; accessing a
@tech{module-level variable} before it is defined signals a run-time @tech{module-level variable} before it is defined signals a run-time
error, just like accessing an undefined global variable. error, just like accessing an undefined global variable.
See also @secref["module-eval-model"] and @secref["mod-parse"]. If a module (in its fully expanded form) does not contain a
@scheme[set!] for an identifier that defined within the module, then
the identifier is a @defterm{constant} after it is defined; its value
cannot be changed afterward, not even through reflective
mechanisms. The @scheme[compile-enforce-module-constants] parameter,
however, can be used to disable enforcement of constants.
When a @tech{syntax object} representing a @scheme[module] form has a When a @tech{syntax object} representing a @scheme[module] form has a
@indexed-scheme['module-language] @tech{syntax property} attached, and @indexed-scheme['module-language] @tech{syntax property} attached, and
@ -186,6 +191,8 @@ be preserved in marshaled bytecode. See also
@scheme[module-compiled-language-info] and @scheme[module-compiled-language-info] and
@scheme[module->language-info].} @scheme[module->language-info].}
See also @secref["module-eval-model"] and @secref["mod-parse"].
@defform[(#%module-begin form ...)]{ @defform[(#%module-begin form ...)]{
Legal only in a @tech{module begin context}, and handled by the Legal only in a @tech{module begin context}, and handled by the