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(slib.info)Requesting Features

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Requesting Features
===================

SLIB creates and maintains a "catalog" mapping features to locations of
files introducing procedures and syntax denoted by those features.

At the beginning of each section of this manual, there is a line like
`(require 'FEATURE)'.  The Scheme files comprising SLIB are cataloged
so that these feature names map to the corresponding files.

SLIB provides a form, `require', which loads the files providing the
requested feature.

 - Procedure: require feature
        * If `(provided? FEATURE)' is true, then `require' just returns
          an unspecified value.

        * Otherwise, if FEATURE is found in the catalog, then the
          corresponding files will be loaded and an unspecified value
          returned.

          Subsequently `(provided? FEATURE)' will return `#t'.

        * Otherwise (FEATURE not found in the catalog), an error is
          signaled.

The catalog can also be queried using `require:feature->path'.

 - Function: require:feature->path feature
        * If FEATURE is already provided, then returns `#t'.

        * Otherwise, if FEATURE is in the catalog, the path or list of
          paths associated with FEATURE is returned.

        * Otherwise, returns `#f'.