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31.3.2 Using Guile Modules

To use a Guile module is to access either its public interface or a custom interface (see General Information about Modules). Both types of access are handled by the syntactic form use-modules, which accepts one or more interface specifications and, upon evaluation, arranges for those interfaces to be available to the current module. This process may include locating and loading code for a given module if that code has not yet been loaded, following %load-path (see Build Config).

An interface specification has one of two forms. The first variation is simply to name the module, in which case its public interface is the one accessed. For example:

(use-modules (ice-9 popen))

Here, the interface specification is (ice-9 popen), and the result is that the current module now has access to open-pipe, close-pipe, open-input-pipe, and so on (see Included Guile Modules).

Note in the previous example that if the current module had already defined open-pipe, that definition would be overwritten by the definition in (ice-9 popen). For this reason (and others), there is a second variation of interface specification that not only names a module to be accessed, but also selects bindings from it and renames them to suit the current module's needs. For example:

(use-modules ((ice-9 popen)
              :select ((open-pipe . pipe-open) close-pipe)
              :renamer (symbol-prefix-proc 'unixy:)))

Here, the interface specification is more complex than before, and the result is that a custom interface with only two bindings is created and subsequently accessed by the current module. The mapping of old to new names is as follows:

(ice-9 popen) sees:             current module sees:
open-pipe                       unixy:pipe-open
close-pipe                      unixy:close-pipe

This example also shows how to use the convenience procedure symbol-prefix-proc.

symbol-prefix-proc prefix-sym Scheme Procedure
Return a procedure that prefixes its arg (a symbol) with prefix-sym.

use-modules spec ... syntax
Resolve each interface specification spec into an interface and arrange for these to be accessible by the current module. The return value is unspecified.

spec can be a list of symbols, in which case it names a module whose public interface is found and used.

spec can also be of the form:

 (MODULE-NAME [:select SELECTION] [:renamer RENAMER])

in which case a custom interface is newly created and used. module-name is a list of symbols, as above; selection is a list of selection-specs; and renamer is a procedure that takes a symbol and returns its new name. A selection-spec is either a symbol or a pair of symbols (ORIG . SEEN), where orig is the name in the used module and seen is the name in the using module. Note that seen is also passed through renamer.

The :select and :renamer clauses are optional. If both are omitted, the returned interface has no bindings. If the :select clause is omitted, renamer operates on the used module's public interface.

Signal error if module name is not resolvable.

use-syntax module-name syntax
Load the module module-name and use its system transformer as the system transformer for the currently defined module, as well as installing it as the current system transformer.