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apply_macros.pl -- Goal expansion rules to avoid meta-calling
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This module defines goal_expansion/2 rules to deal with commonly used, but fundamentally slow meta-predicates. Notable maplist/2... defines a useful set of predicates, but its execution is considerable slower than a traditional Prolog loop. Using this library calls to maplist/2... are translated into an call to a generated auxiliary predicate that is compiled using compile_aux_clauses/1. Currently this module supports:

The idea for this library originates from ECLiPSe and came to SWI-Prolog through YAP.

- Jan Wielemaker
To be done
- Support more predicates
Source expand_maplist(+Callable, +Lists, -Goal) is det[private]
Macro expansion for maplist/2 and higher arity. The first clause deals with code using maplist on fixed lists to reduce typing. Note that we only expand if all lists have fixed length. In theory we only need at least one of fixed length, but in that case the goal expansion instantiates variables in the clause, causing issues with the remainder of the clause expansion mechanism.
Source maplist_extend_goal(+Closure, +Args, -Goal) is semidet[private]
Extend the maplist Closure with Args. This can be tricky. Notably library(yall) lambda expressions may instantiate the Closure while the real execution does not. We can solve that by using lambda_calls/3. The expand_goal_no_instantiate/2 ensures safe goal expansion.
Source expand_closure_no_fail(+Goal, +Extra:integer, -GoalExt) is det[private]
Add Extra additional arguments to Goal.
Source expand_apply(+GoalIn:callable, -GoalOut) is semidet[private]
Macro expansion for `apply' predicates.
Source expand_apply(+GoalIn:callable, -GoalOut, +PosIn, -PosOut) is semidet[private]
Translation of simple meta calls to inline code while maintaining position information. Note that once(Goal) cannot be translated to (Goal->true) because this will break the compilation of (once(X) ; Y). A correct translation is to (Goal->true;fail). Abramo Bagnara suggested ((Goal->true),true), which is both faster and avoids warning if style_check(+var_branches) is used.
Source expand_phrase(+PhraseGoal, -Goal) is semidet
Source expand_phrase(+PhraseGoal, +Pos0, -Goal, -Pos) is semidet
Provide goal-expansion for PhraseGoal. PhraseGoal is either phrase/2,3 or call_dcg/2,3. The current version does not translate control structures, but only simple terminals and non-terminals.

For example:

?- expand_phrase(phrase(("ab", rule)), List), Goal).
Goal = (List=[97, 98|_G121], rule(_G121, [])).
- Re-throws errors from dcg_translate_rule/2
Source dcg_extend(+Callable, +Pos0, -Goal, -Pos, +Xs0, ?Xs) is semidet[private]
Source qcall_instantiated(@Term) is semidet[private]
True if Term is instantiated sufficiently to call it.
To be done
- Shouldn't this be callable straight away?
Source apply_macros_sentinel
Used to detect that library(apply_macros) is loaded into the current context explicitly. This test is used if the Prolog flag apply_macros is set to imported.