3.21.6 Remarks on the library(http/html_write) library

This library is the result of various attempts to reach at a more satisfactory and Prolog-minded way to produce HTML text from a program. We have been using Prolog for the generation of web pages in a number of projects. Just using format/2 never was not a real option, generating error-prone HTML from clumsy syntax. We started with a layer on top of format/2, keeping track of the current nesting and thus always capable of properly closing the environment.

DCG based translation however, naturally exploits Prolog's term-rewriting primitives. If generation fails for whatever reason it is easy to produce an alternative document (for example holding an error message).

In a future version we will probably define a goal_expansion/2 to do compile-time optimisation of the library. Quotation of known text and invocation of sub-rules using the \RuleSet and <Module>:<RuleSet> operators are costly operations in the analysis that can be done at compile-time.