From 0f347162b74d945f509955b6c57e506ab800db7b Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <peter@pmikkelsen.com>
Date: Thu, 22 Jul 2021 19:35:53 +0000
Subject: Implement halt/0, halt/1, and understand the --no-repl flag

---
 builtins.c | 17 +++++++++++++++++
 loader.pl  |  5 ++++-
 repl.pl    | 12 +++++-------
 stdlib.pl  | 10 ++++++++++
 4 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/builtins.c b/builtins.c
index d1f70b9..79c71f0 100644
--- a/builtins.c
+++ b/builtins.c
@@ -70,6 +70,7 @@ BuiltinProto(builtinsetstreamposition);
 BuiltinProto(builtinop);
 BuiltinProto(builtincurrentops);
 BuiltinProto(builtinnewemptymodule);
+BuiltinProto(builtinhalt);
 
 int compareterms(Term *, Term *);
 
@@ -199,6 +200,8 @@ findbuiltin(Term *goal)
 		return builtincurrentops;
 	if(Match(L"$new_empty_module", 1))
 		return builtinnewemptymodule;
+	if(Match(L"$halt", 1))
+		return builtinhalt;
 
 	return nil;
 }
@@ -1649,3 +1652,17 @@ builtinnewemptymodule(Term *goal, Binding **bindings, Module *module)
 	addemptymodule(name);
 	return 1;
 }
+
+int
+builtinhalt(Term *goal, Binding **bindings, Module *module)
+{
+	USED(bindings);
+	USED(module);
+	vlong exitcode = goal->children->ival;
+	char *msg = nil;
+	if(exitcode != 0)
+		msg = smprint("pprolog exit code: %lld\n", exitcode);
+
+	exits(msg);
+	return 1;
+}
diff --git a/loader.pl b/loader.pl
index 0a9f8df..99478d0 100644
--- a/loader.pl
+++ b/loader.pl
@@ -2,7 +2,10 @@
 
 start(Args) :-
 	catch((load_module_from_file('/sys/lib/prolog/repl.pl'), ReplLoaded = true), E, (print_exception(E), ReplLoaded = false)),
-	( ReplLoaded = true-> repl:repl(Args) ).
+	!,
+	( ReplLoaded = true
+	-> repl:repl(Args)
+	).
 
 print_exception(E) :-
 	write('Caught exception while loading /sys/lib/prolog/repl.pl: '),
diff --git a/repl.pl b/repl.pl
index 0bb279f..8f68551 100644
--- a/repl.pl
+++ b/repl.pl
@@ -1,17 +1,15 @@
 :- module(repl, []).
 
 repl([_ProgName|Args]) :-
-	write('Welcome to p-prolog version 1.'),
-	nl,
-	write('Started with args: '),
-	write(Args),
-	nl,
-	flush_output,
 	handle_args(Args),
-	repl_loop.
+	( member('--no-repl', Args)
+	-> halt
+	; repl_loop
+	).
 
 handle_arg('-d') :-
 	set_prolog_flag(debug, on).
+handle_arg('--no-repl').
 handle_arg(Arg) :-
 	loader:load_module_from_file(Arg).
 
diff --git a/stdlib.pl b/stdlib.pl
index bca7e31..19b20d0 100644
--- a/stdlib.pl
+++ b/stdlib.pl
@@ -683,6 +683,16 @@ current_op(Priority, Op_specifier, Operator) :-
 	current_ops(Operators),
 	member(op(Priority, Op_specifier, Operator), Operators).
 
+% Halting
+
+halt(X) :-
+	is_nonvar(X),
+	is_integer(X),
+	'$halt'(X).
+
+halt :-
+	halt(0).
+
 % Loading prolog text
 
 consult(File) :-
-- 
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