7.10.4 Caches

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The cache of a page is an array C with the following properties:

In particular, C[C[0]] is the rack of a page with cache C.

The Logiweb system provides access to the cache of a page in several ways:

For the unpacker and macro expander, the cache is not yet complete. Rather, the output of the unpacker and macro expander is hung on the 'body' and 'expansion' hook, respectively, of the rack of the page being loaded.

The output of the verifier is hung on the diagnose hook but, as mentioned, the output is included lazily before it is computed so that the verifier thinks it has access to the complete cache. That is important since if the verifier deems a cache correct or incorrect, and if the cache is then changed by adding or not adding a diagnose, then the conclusion of the verifier may be incorrect relative to the final value of the cache. This cannot happen when the diagnose is added lazily. As an example, if the verifier accesses the diagnose in order to say e.g. 'the page is correct iff it is incorrect' then the verifier will loop indefinitely and, thus, it will never make up its mind whether or not the cache is correct.

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