7.14 Unpacking

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Unpacking is one of the four, user defined functions which are invoked by lgc(1). The way it is invoked is similar to the way the verifier, macro engine, and renderer are invoked. A page is unpacked thus:

Contrary to verification and macro expansion, the pages described here do not define their own unpacker. Rather, they rely on the default unpacker. The default unpacker is defined as part of the lgc compiler and thus appears on the lgc page.

Contrary to verification, macro expansion, and rendering, lgc only looks for an unpacker on the bed page. A page cannot define its own unpacker: the unpacker produces the body and the body contains the definitions. Thus, even if a page defines an unpacker, lgc cannot know the unpacker before the page is unpacked.

The notion of an unpacker allows users to define alternative formats for storing the body of Logiweb pages. As an example, the notion of an unpacker allows to introduce pages that are compressed and/or encrypted. The format of the bibliography and dictionary of a Logiweb page is fixed.

For an example of an unpacker, untar the tar ball, cd to src/testsuite/port, and look at unpacker.lgs and unpacked.lgs.

At present, the notion of an unpacker is not very useful since lgc can only generate pages in the default format.

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Copyright © 2010 Klaus Grue, GRD-2010-01-05