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R5RS discusses how to structure programs. Everything which is defined
in Section 5 of R5RS applies also to STklos. To make things
shorter, this aspects will not be described here (see R5RS for
complete information). STklos modules can be used to organize a program into separate
environments (or name spaces). Modules provide a clean way to
organize and enforce the barriers between the components of a program. STklos provides a simple module system which is largely inspired from
the one of Tung and Dybvig exposed in [14]. As their
modules system, STklos modules are defined to be easily used in an
interactive environment.
(define-module <name> <expr1> <expr2> ...) | STklos syntax |
Define-module evaluates the expressions <expr1>, <expr2> ... which
constitute the body of the module <name> in the environment of that module.
Name must be a valid symbol. If this symbol has not already been used to
define a module, a new module, named name, is created.
Otherwise, the expressions <expr1>, <expr2> ... are evaluated in
the environment of the (old) module <name>
1.
Definitions done in a module are local to the module and do not interact with
the definitions in other modules. Consider the following definitions,
(define-module M1
(define a 1))
(define-module M2
(define a 2)
(define b (* 2 x)))
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Here, two modules are defined and they both bind the symbol a to a
value. However, since a has been defined in two distinct modules
they denote two different locations.
The STklos module, which is predefined, is a special module which
contains all the global variables of a R5RS program. A symbol
defined in the STklos module, if not hidden by a local definition, is
always visible from inside a module. So, in the previous exemple, the
x symbol refers the x symbol defined in the STklos module.
The result of define-module is void. |
(current-module) | STklos procedure |
Returns the current module.
(define-module M
(display
(cons (eq? (current-module) (find-module 'M))
(eq? (current-module) (find-module 'STklos)))))
-| (#t . #f)
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(find-module name) | STklos procedure |
(find-module name default)
STklos modules are first class objects and find-module returns the
module associated to name if it exists. If there is no module
associated to name, an error is signaled if no default is
provided, otherwise find-module returns default. |
(module? object) | STklos procedure |
Returns #t if object is a module and #f otherwise.
(module? (find-module 'STklos)) ⇒ #t
(module? 'STklos) ⇒ #f
(module? 123 'no) ⇒ no
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(export <symbol1> <symbol2> ...) | STklos syntax |
Specifies the symbols which are exported (i.e. visible) outside
the current module. By default, symbols defined in a module are not
visible outside this module, excepted if they appear in an export
clause.
If several export clauses appear in a module, the set of
exported symbols is determined by ``unionizing'' symbols exported
in all the export clauses.
The result of export is void. |
(import <module1> <module2> ...) | STklos syntax |
Specifies the modules which are imported by the current module.
Importing a module makes the symbols it exports visible to the
importer, if not hidden by local definitions. When a symbol
is exported by several of the imported modules, the location denoted by
this symbol in the importer module correspond to the one of the first module
in the list
(<module1> <module2> ...)
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which exports it.
If several import clauses appear in a module, the set of
imported modules is determined by appending the various list of modules
in their apparition order.
(define-module M1
(export a b)
(define a 'M1-a)
(define b 'M1-b))
(define-module M2
(export b c d)
(define b 'M2-b)
(define c 'M2-c)
(define d 'M2-d))
(define-module M3
(import M1 M2)
(display (list a b c d))) -| (M1-a M1-b M2-c M2-d)
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(define-module M4
(import M2 M1)
(display (list a b c d))) -| (M1-a M2-b M2-c M2-d)
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(select-module <name>) | STklos syntax |
Changes the value of the current module to the module with the given name.
The expressions evaluated after select-module will take place in
module name environment. Module name must have been created
previously by a define-module. The result of select-module is
void.
Select-module is particularly useful when debugging since it
allows to place toplevel evaluation in a particular module. The
following transcript shows an usage of select-module.
2:
stklos> (define foo 1)
stklos> (define-module bar
(define foo 2))
stklos> foo
1
stklos> (select-module bar)
bar> foo
2
bar> (select-module stklos)
stklos>
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(symbol-value symbol module) | STklos procedure |
(symbol-value symbol module default)
Returns the value bound to symbol in module. If symbol is not bound,
an error is signaled if no default is provided, otherwise symbol-value
returns default. |
(symbol-value* symbol module) | STklos procedure |
(symbol-value* symbol module default)
Returns the value bound to symbol in module. If symbol is not bound,
an error is signaled if no default is provided, otherwise symbol-value
returns default.
Note that this function searches the value of symbol in module
and all the modules it imports whereas symbol-value searches
only in module. |
(module-name module) | STklos procedure |
Returns the name (a symbol) associated to a module. |
(module-imports module) | STklos procedure |
Returns the list of modules that module (fully) imports. |
(module-exports module) | STklos procedure |
Returns the list of symbols exported by module. Note that this function
returns the list of symbols given in the module export clause and that
some of these symbols can be not yet defined. |
(module-symbols module) | STklos procedure |
Returns the list of symbols already defined in module. |
(all-modules) | STklos procedure |
Returns the list of all the living modules. |
(in-module mod s) | STklos syntax |
(in-module mod s default)
This form returns the value of symbol with name s in the module with name
mod. If this symbol is not bound, an error is signaled if no default is
provided, otherwise in-module returns default. Note that the value of s
is searched in mod and all the modules it imports.
This form is in fact a shortcut. In effect,
(in-module my-module foo)
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is equivalent to
(symbol-value* 'foo (find-module 'my-module))
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1: In fact define-module on a given name
defines a new module only the first time it is invoked on this name.
By this way, interactively reloading a module does not define
a new entity, and the other modules which use it are not altered.
2: This transcript uses the default toplevel loop
which displays the name of the current module in the evaluator
prompt.
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