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(slib.info)Require

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Require
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 - Variable: *features*
     Is a list of symbols denoting features supported in this
     implementation.  *FEATURES* can grow as modules are `require'd.
     *FEATURES* must be defined by all implementations (Note:
     Porting).

     Here are features which SLIB (`require.scm') adds to *FEATURES*
     when appropriate.

        * 'inexact

        * 'rational

        * 'real

        * 'complex

        * 'bignum

     For each item, `(provided? 'FEATURE)' will return `#t' if that
     feature is available, and `#f' if not.

 - Variable: *modules*
     Is a list of pathnames denoting files which have been loaded.

 - Variable: *catalog*
     Is an association list of features (symbols) and pathnames which
     will supply those features.  The pathname can be either a string
     or a pair.  If pathname is a pair then the first element should be
     a macro feature symbol, `source', or `compiled'.  The cdr of the
     pathname should be either a string or a list.

In the following functions if the argument FEATURE is not a symbol it
is assumed to be a pathname.

 - Function: provided? feature
     Returns `#t' if FEATURE is a member of `*features*' or `*modules*'
     or if FEATURE is supported by a file already loaded and `#f'
     otherwise.

 - Procedure: require feature
     FEATURE is a symbol.  If `(provided? FEATURE)' is true `require'
     returns.  Otherwise, if `(assq FEATURE *catalog*)' is not `#f',
     the associated files will be loaded and `(provided? FEATURE)' will
     henceforth return `#t'.  An unspecified value is returned.  If
     FEATURE is not found in `*catalog*', then an error is signaled.

 - Procedure: require pathname
     PATHNAME is a string.  If PATHNAME has not already been given as
     an argument to `require', PATHNAME is loaded.  An unspecified
     value is returned.

 - Procedure: provide feature
     Assures that FEATURE is contained in `*features*' if FEATURE is a
     symbol and `*modules*' otherwise.

 - Function: require:feature->path feature
     Returns `#t' if FEATURE is a member of `*features*' or `*modules*'
     or if FEATURE is supported by a file already loaded.  Returns a
     path if one was found in `*catalog*' under the feature name, and
     `#f' otherwise.  The path can either be a string suitable as an
     argument to load or a pair as described above for *catalog*.