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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
be executed more efficiently.
Along the same lines, re-declaration of a module is not generally
allowed. Indeed, for file-based modules, simply changing the file does
not lead to a re-declaration, because file-based modules are loaded on
Along the same lines, when a module contains no @scheme[set!] of a
particular identifier that is defined within the module, then the
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
requests. It is possible to use Scheme's reflection support to
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
involves the re-definition of a previously immutable binding.
in the @tech{REPL}; in such cases, the re-declaration may fail if it
involves the re-definition of a previously constant binding.
@interaction[
(module m scheme

11
collects/scribblings/reference/syntax.scrbl
View File

@ -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
expressions in the body of the module. Evaluation merely declares a
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
@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
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
@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->language-info].}
See also @secref["module-eval-model"] and @secref["mod-parse"].
@defform[(#%module-begin form ...)]{
Legal only in a @tech{module begin context}, and handled by the