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13.4.1 Resolving Module Names
13.4.2 Compiled Modules and References
13.4.3 Dynamic Module Access

13.4 Module Names and Loading

13.4.1 Resolving Module Names

The name of a declared module is represented by a resolved module path, which encapsulates either a symbol or a complete filesystem path (see Paths). A symbol normally refers to a predefined module or module declared through reflective evaluation (e.g., eval). A filesystem path normally refers to a module declaration that was loaded on demand via require or other forms.

A module path is a datum that matches the grammar for module-path for require. A module path is relative to another module.

Returns #f if v is a resolved module path, #f otherwise.

Returns a resolved module path that encapsulates path. If path is not a symbol, it normally should be cleansed (see cleanse-path) and simplified (see simplify-path).

A resolved module path is interned. That is, if two resolved module path values encapsulate paths that are equal?, then the resolved module path values are eq?.

(resolved-module-path-name module-path)  (or/c path? symbol?)
  module-path : resolved-module-path?
Returns the path or symbol encapsulated by a resolved module path.

(module-path? v)  boolean?
  v : any/c
Returns #t if v corresponds to a datum that matches the grammar for module-path for require, #f otherwise.

A parameter that determines the current module name resolver, which manages the conversion from other kinds of module references to a resolved module path. For example, when the expander encounters (require module-path) where module-path is not an identifier, then the expander passes 'module-path to the module name resolver to obtain a symbol or resolved module path. When such a require appears within a module, the module path resolver is also given the name of the enclosing module, so that a relative reference can be converted to an absolute symbol or resolved module path.

A module name resolver takes one and four arguments:
  • When given one argument, it is a name for a module declaration that is already loaded. Such a call to the module name resolver is a notification that the corresponding module does not need to be loaded (for the current namespace, or any other namespace that shares the same module registry). The module name resolver’s result is ignored.

  • When given four arguments, the first is a module path, either equivalent to a quoted module-path for require or a file system path. The second is name for the source module, if any, to which the path is relative; if the second argument is #f, the module path is relative to (or (current-load-relative-directory) (current-directory)). The third argument is a syntax object that can be used for error reporting, if it is not #f. If the last argument is #t, then the module declaration should be loaded (if it is not already), otherwise the module path should be simply resolved to a name. The result is the resolved name.

For the second case, the standard module name resolver keeps a per-registry table of loaded module name. If a resolved module path is not in the table, and #f is not provided as the third argument to the module name resolver, then the name is put into the table and the corresponding file is loaded with a variant of load/use-compiled that passes the expected module name to the compiled-load handler.

While loading a file, the default module name resolver sets the current-module-declare-name parameter to the resolved module name (while the compiled-load handler sets current-module-declare-source). Also, the default module name resolver records in a private continuation mark the module being loaded, and it checks whether such a mark already exists; if such a continuation mark does exist in the current continuation, then the exn:fail exception is raised with a message about a dependency cycle.

Module loading is suppressed (i.e., #f is supplied as a third argument to the module name resolver) when resolving module paths in syntax objects (see Syntax Objects). When a syntax object is manipulated, the current namespace might not match the original namespace for the syntax object, and the module should not necessarily be loaded in the current namespace.

The current module name resolver is called with a single argument by namespace-attach-module to notify the resolver that a module was attached to the current namespace (and should not be loaded in the future for the namespace’s registry). No other Racket operation invokes the module name resolver with a single argument, but other tools (such as DrRacket) might call this resolver in this mode to avoid redundant module loads.

A parameter that determines a module name that is used when evaluating a module declaration (when the parameter value is not #f). In that case, the id from the module declaration is ignored, and the parameter’s value is used as the name of the declared module.

A parameter that determines source information to be associated with a module when evaluating a module declaration. Source information is used in error messages and reflected by variable-reference->module-source. When the parameter value is #f, the module’s name (as determined by current-module-declare-name) is used as the source name instead of the parameter value.

13.4.2 Compiled Modules and References

While expanding a module declaration, the expander resolves module paths for imports to load module declarations as necessary and to determine imported bindings, but the compiled form of a module declaration preserves the original module path. Consequently, a compiled module can be moved to another filesystem, where the module name resolver can resolve inter-module references among compiled code.

When a module reference is extracted from compiled form (see module-compiled-imports) or from syntax objects in macro expansion (see Syntax Object Content), the module reference is reported in the form of a module path index. A module path index is a semi-interned (multiple references to the same relative module tend to use the same module path index value, but not always) opaque value that encodes a module path (see module-path?) and either a resolved module path or another module path index to which it is relative.

A module path index that uses both #f for its path and base module path index represents “self”—i.e., the module declaration that was the source of the module path indexand such a module path index can be used as the root for a chain of module path indexes at compile time. For example, when extracting information about an identifier’s binding within a module, if the identifier is bound by a definition within the same module, the identifier’s source module is reported using the “self” module path index. If the identifier is instead defined in a module that is imported via a module path (as opposed to a literal module name), then the identifier’s source module will be reported using a module path index that contains the required module path and the “self” module path index.

A module path index has state. When it is resolved to a resolved module path, then the resolved module path is stored with the module path index. In particular, when a module is loaded, its root module path index is resolved to match the module’s declaration-time name. This resolved path is forgotten, however, in identifiers that the module contributes to the compiled and marshaled form of other modules. The transient nature of resolved names allows the module code to be loaded with a different resolved name than the name when it was compiled.

(module-path-index? v)  boolean?
  v : any/c
Returns #t if v is a module path index, #f otherwise.

Returns a resolved module path for the resolved module name, computing the resolved name (and storing it in mpi) if it has not been computed before.

Resolving a module path index uses the current module name resolver (see current-module-name-resolver). Depending on the kind of module paths encapsulated by mpi, the computed resolved name can depend on the value of current-load-relative-directory or current-directory.

Returns two values: a module path, and a base module path index or #f to which the module path is relative.

A #f second result means that the path is relative to an unspecified directory (i.e., its resolution depends on the value of current-load-relative-directory and/or current-directory).

A #f for the first result implies a #f for the second result, and means that mpi represents “self” (see above).

Combines path and mpi to create a new module path index. The path argument can #f only if mpi is also #f.

Returns #t if v is a compiled module declaration, #f otherwise. See also current-compile.

(module-compiled-name compiled-module-code)  symbol?
  compiled-module-code : compiled-module-expression?
Takes a module declaration in compiled form and returns a symbol for the module’s declared name.

(module-compiled-imports compiled-module-code)
(listof (cons/c (or/c exact-integer? #f)
                (listof module-path-index?)))
  compiled-module-code : compiled-module-expression?
Takes a module declaration in compiled form and returns an association list mapping phase level shifts (where #f corresponds to a shift into the label phase level) to module references for the module’s explicit imports.

(module-compiled-exports compiled-module-code)
(listof (cons/c (or/c exact-integer? #f) list?))
(listof (cons/c (or/c exact-integer? #f) list?))
  compiled-module-code : compiled-module-expression?

Returns two association lists mapping phase level values (where #f corresponds to the label phase level) to exports at the corresponding phase. The first association list is for exported variables, and the second is for exported syntax. Beware however, that value bindings re-exported though a rename transformer are in the syntax list instead of the value list.

Each associated list, which is represented by list? in the result contracts above, more precisely matches the contract

(listof (list/c symbol?
                 (or/c module-path-index?
                       (list/c module-path-index?
                               (or/c exact-integer? #f)
                               (or/c exact-integer? #f))))))

For each element of the list, the leading symbol is the name of the export.

The second part—the list of module path index values, etc.—describes the origin of the exported identifier. If the origin list is null, then the exported identifier is defined in the module. If the exported identifier is re-exported, instead, then the origin list provides information on the import that was re-exported. The origin list has more than one element if the binding was imported multiple times from (possibly) different sources.

For each origin, a module path index by itself means that the binding was imported with a phase level shift of 0 (i.e., a plain require without for-meta, for-syntax, etc.), and imported identifier has the same name as the re-exported name. An origin represented with a list indicates explicitly the import, the import phase level shift (where #f corresponds to a for-label import), the import name of the re-exported binding, and the phase level of the import.}

(module-compiled-language-info compiled-module-code)
  (or/c #f (vector/c module-path? symbol? any/c))
  compiled-module-code : compiled-module-expression?

Returns information intended to reflect the “language” of the module’s implementation as originally attached to the syntax of the module’s declaration though the 'module-language syntax property. See also module.

If no information is available for the module, the result is #f. Otherwise, the result is (vector mp name val) such that ((dynamic-require mp name) val) should return function that takes two arguments. The function’s arguments are a key for reflected information and a default value. Acceptable keys and the interpretation of results is up to external tools, such as DrRacket. If no information is available for a given key, the result should be the given default value.

See also module->language-info and racket/language-info.

13.4.3 Dynamic Module Access

(dynamic-require mod provided [fail-thunk])  any
  mod : 
(or/c module-path?
  provided : (or/c symbol? #f 0 void?)
  fail-thunk : (-> any) = (lambda () ....)
Dynamically instantiates the module specified by mod in the current namespace’s registry at the namespace’s base phase, if it is not yet instantiated. The current module name resolver may load a module declaration to resolve mod (see current-module-name-resolver); the path is resolved relative to current-load-relative-directory and/or current-directory.

If provided is #f, then the result is #<void>, and the module is not visited (see Module Phases and Visits) or even made available (for on-demand visits) in phases above the base phase.

When provided is a symbol, the value of the module’s export with the given name is returned, and still the module is not visited or made available in higher phases. If the module exports provided as syntax, then a use of the binding is expanded and evaluated in a fresh namespace to which the module is attached, which means that the module is visited in the fresh namespace. If the module has no such exported variable or syntax, then fail-thunk is called; the default fail-thunk raises exn:fail:contract. If the variable named by provided is exported protected (see Code Inspectors), then the exn:fail:contract exception is raised.

If provided is 0, then the module is instantiated but not visited, the same as when provided is #f. With 0, however, the module is made available in higher phases.

If provided is #<void>, then the module is visited but not instantiated (see Module Phases and Visits), and the result is #<void>.

(dynamic-require-for-syntax mod    
  [fail-thunk])  any
  mod : module-path?
  provided : (or/c symbol? #f)
  fail-thunk : (-> any) = (lambda () ....)
Like dynamic-require, but in a phase that is 1 more than the namespace’s base phase.

(module->language-info mod [load?])
  (or/c #f (vector/c module-path? symbol? any/c))
  mod : (or/c module-path? path? resolved-module-path?)
  load? : any/c = #f
Returns information intended to reflect the “language” of the implementation of mod. If load? is #f, the module named by mod must be declared (but not necessarily instantiated or visited) in the current namespace; otherwise, mod may be loaded (as for dynamic-require and other functions). The information returned by module->language-info is the same as would have been returned by module-compiled-language-info applied to the module’s implementation as compiled code.

(module->imports mod)
(listof (cons/c (or/c exact-integer? #f)
                (listof module-path-index?)))
  mod : (or/c module-path? path? resolved-module-path?)
Like module-compiled-imports, but produces the imports of mod, which must be declared (but not necessarily instantiated or visited) in the current namespace.

Like module-compiled-exports, but produces the exports of mod, which must be declared (but not necessarily instantiated or visited) in the current namespace.