This module provides the term-expansion rules for DCGs as well as phrase/2,3 and call_dcg/3 for calling DCGs. The original code was copied from C-Prolog and written by Fernando Pereira, EDCAAD, Edinburgh, 1984. Since then many people have modified and extended this code.

DCGs have for a long time been a moving target, notably when it comes to dealing with cuts and unification delaying for calls to non-DCG code. This has slowly converged. This implementation attempts to be closely compatible to the pending ISO standard for DCGs.

 dcg_body(:DCG, ?Pos0, +Qualify, ?List, ?Tail, -Goal, -Pos) is det[private]

Translate DCG body term.

 qualify(+QualifyInfo, +Goal, +Pos0, -QGoal, -Pos) is det[private]

Arguments:

QualifyInfo

- is a term q(Module,Context,Pos), where Module is the module in which Goal must be called and Context is the current source module.

 dcg_extend(+Head, +Extra1, +Extra2, -NewHead)[private]

Extend Head with two more arguments (on behalf DCG compilation). The solution below is one option. Using =.. and append is the alternative. In the current version (5.3.2), the =.. is actually slightly faster, but it creates less garbage.

 dcg_extend(:Rule, ?Pos0, ?List, ?Tail, -Head, -Pos) is det[private]

Extend a non-terminal with the DCG difference list List\Tail. The position term is extended as well to reflect the layout of the created term. The additional variables are located at the end of the Rule.

 dcg_bt_pos(?BraceTermPos, -Pos) is det[private]

Position transformation for mapping of {G} to (G, S=SR).

 dcg_terminal_pos(+ListPos, -TermPos)[private]

 dcg_qualify_pos(?TermPos0, ?ModuleCreatingPos, -TermPos)[private]

 phrase(:RuleSet, ?List)

 phrase(:RuleSet, ?List, ?Rest)

Interface to DCGs

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 dcg_translate_rule(Arg1, Arg2, Arg3, Arg4)

 phrase(Arg1, Arg2, Arg3)

 call_dcg(Arg1, Arg2, Arg3)

 dcg_translate_rule(Arg1, Arg2)