From e702fe5c686ae1ddf3936a557ed0cb816d5f344f Mon Sep 17 00:00:00 2001
From: Markus Triska <triska@metalevel.at>
Date: Sat, 6 Jan 2024 09:21:22 +0100
Subject: [PATCH] ADDED: Support for higher-order non-terminals phrase//[2,3]

These non-terminals take a grammar rule body and additional arguments
as arguments. These arguments are appended to the first argument.

A key motivation for the introduction of these non-terminals is found
in the discussion and sample code provided by @bakaq in:

    https://github.com/mthom/scryer-prolog/discussions/2260

In this way, portable higher-order DCG programming is possible while
keeping the logical grammar rule expansion implementation dependent.

Example:

    ?- phrase(phrase('.', a, []), Cs).
       Cs = "a".
---
 src/lib/dcgs.pl | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/src/lib/dcgs.pl b/src/lib/dcgs.pl
index ef2e82533..9f7dfacfb 100644
--- a/src/lib/dcgs.pl
+++ b/src/lib/dcgs.pl
@@ -12,6 +12,8 @@
           [op(1105, xfy, '|'),
            phrase/2,
            phrase/3,
+           phrase/4,
+           phrase/5,
            seq//1,
            seqq//1,
            ... //0,
@@ -27,6 +29,10 @@
 
 :- meta_predicate phrase(2, ?, ?).
 
+:- meta_predicate phrase(2, ?, ?, ?).
+
+:- meta_predicate phrase(2, ?, ?, ?, ?).
+
 %% phrase(+Body, ?Ls).
 %
 % True iff Body describes the list Ls. Body must be a DCG body.
@@ -76,6 +82,34 @@
     ;  call(M:GRBody1, S0, S)
     ).
 
+phrase(GRBody, Arg, S0, S) :-
+    strip_module(GRBody, M, GRBody1),
+    (  var(GRBody) ->
+       instantiation_error(phrase/4)
+    ;  nonvar(GRBody1),
+       GRBody1 =.. GRBodys1,
+       append(GRBodys1, [Arg], GRBodys2),
+       GRBody2 =.. GRBodys2,
+       dcg_constr(GRBody2),
+       dcg_body(GRBody2, S0, S, GRBody3) ->
+       call(M:GRBody3)
+    ;  call(M:GRBody1, Arg, S0, S)
+    ).
+
+phrase(GRBody, Arg1, Arg2, S0, S) :-
+    strip_module(GRBody, M, GRBody1),
+    (  var(GRBody) ->
+       instantiation_error(phrase/5)
+    ;  nonvar(GRBody1),
+       GRBody1 =.. GRBodys1,
+       append(GRBodys1, [Arg1,Arg2], GRBodys2),
+       GRBody2 =.. GRBodys2,
+       dcg_constr(GRBody2),
+       dcg_body(GRBody2, S0, S, GRBody3) ->
+       call(M:GRBody3)
+    ;  call(M:GRBody1, Arg1, Arg2, S0, S)
+    ).
+
 % The same version of the below two dcg_rule clauses, but with module scoping.
 dcg_rule(( M:NonTerminal, Terminals --> GRBody ), ( M:Head :- Body )) :-
     dcg_non_terminal(NonTerminal, S0, S, Head),
@@ -139,6 +173,8 @@
 dcg_constr({_}). % 7.14.7
 dcg_constr(call(_)). % 7.14.8
 dcg_constr(phrase(_)). % 7.14.9
+dcg_constr(phrase(_,_)). % extension of 7.14.9
+dcg_constr(phrase(_,_,_)). % extension of 7.14.9
 dcg_constr(!). % 7.14.10
 %% dcg_constr(\+ _). % 7.14.11 - not (existence implementation dep.)
 dcg_constr((_->_)). % 7.14.12 - if-then (existence implementation dep.)
@@ -166,6 +202,8 @@
 dcg_cbody({Goal}, S0, S, ( Goal, S0 = S )).
 dcg_cbody(call(Cont), S0, S, call(Cont, S0, S)).
 dcg_cbody(phrase(Body), S0, S, phrase(Body, S0, S)).
+dcg_cbody(phrase(Body, Arg), S0, S, phrase(Body, Arg, S0, S)).
+dcg_cbody(phrase(Body, Arg1, Arg2), S0, S, phrase(Body, Arg1, Arg2, S0, S)).
 dcg_cbody(!, S0, S, ( !, S0 = S )).
 % dcg_cbody(\+ GRBody, S0, S, ( \+ phrase(GRBody,S0,_), S0 = S )).
 dcg_cbody(( GRIf -> GRThen ), S0, S, ( If -> Then )) :-