From 50f83a91220940042962fdb55d07bb03991f52be Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <peter@pmikkelsen.com>
Date: Wed, 30 Jun 2021 17:03:25 +0000
Subject: Add support for builtins, and implement true/0, fail/0, call/1, and
 !/0 builtins

---
 builtins.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 builtins.c

(limited to 'builtins.c')

diff --git a/builtins.c b/builtins.c
new file mode 100644
index 0000000..5db5e62
--- /dev/null
+++ b/builtins.c
@@ -0,0 +1,92 @@
+#include <u.h>
+#include <libc.h>
+
+#include "dat.h"
+#include "fns.h"
+
+int builtintrue(Term *, Term *, Goal **, Choicepoint **, Binding **);
+int builtinfail(Term *, Term *, Goal **, Choicepoint **, Binding **);
+int builtincall(Term *, Term *, Goal **, Choicepoint **, Binding **);
+int builtincut(Term *, Term *, Goal **, Choicepoint **, Binding **);
+
+Builtin
+findbuiltin(Term *goal)
+{
+	int arity;
+	Rune *name;
+
+	switch(goal->tag){
+	case AtomTerm:
+		arity = 0;
+		name = goal->text;
+		break;
+	case CompoundTerm:
+		arity = goal->arity;
+		name = goal->text;
+		break;
+	default:
+		return nil;
+	}
+
+	if(!runestrcmp(name, L"true") && arity == 0)
+		return builtintrue;
+	if(!runestrcmp(name, L"fail") && arity == 0)
+		return builtinfail;
+	if(!runestrcmp(name, L"call") && arity == 1)
+		return builtincall;
+	if(!runestrcmp(name, L"!") && arity == 0)
+		return builtincut;
+
+	return nil;
+}
+
+int
+builtintrue(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(goal);
+	USED(goals);
+	USED(choicestack);
+	USED(bindings);
+	return 1;
+}
+
+int
+builtinfail(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(goal);
+	USED(goals);
+	USED(choicestack);
+	USED(bindings);
+	return 0;
+}
+
+int
+builtincall(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(choicestack);
+	USED(bindings);
+
+	Goal *g = malloc(sizeof(Goal));
+	g->goal = goal->children;
+	g->next = *goals;
+	*goals = g;
+
+	return 1;
+}
+
+int
+builtincut(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(goals);
+	USED(bindings);
+
+	Choicepoint *cp = *choicestack;
+	while(cp != nil && cp->id == goal->clausenr)
+		cp = cp->next;
+	*choicestack = cp;
+	return 1;
+}
\ No newline at end of file
-- 
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