Internal Clause Rewriting¶

YAP supports several clause optimisation mechanisms, that are designed to improve execution of arithmetic and term construction built-ins.

In other words, during the compilation process a clause is rewritten twice:

1. first, perform user-defined goal_expansion as described in the predicates goal_expansion//11 and goal_expansion//22.

2. Perform expansion of some built-ins like:

3. pruning operators, like ->//22 and F>//22

4. arithmetic, including early evaluation of constant expressions

5. specialise versions for some built-ins, if we are aware of the run-time execution mode

The user has some control over this process, through some built-ins and through execution flsgs.

• contains_illegal_dcgnt/1
• do_not_compile_expressions/0
• compile_expressions/0
• expand_exprs/2

Functions:¶

1. *** prolog::contains_illegal_dcgnt(+Term) is semidet.%% True if Term contains a non-terminal we cannot deal with using% goal-expansion. The test is too general approximation*: