From 480de114963ecee700ece5b8793916726c04b9ab Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <peter@pmikkelsen.com>
Date: Fri, 16 Jul 2021 15:25:01 +0000
Subject: Replace the C repl with one written in prolog :)

---
 repl.pl | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 repl.pl

(limited to 'repl.pl')

diff --git a/repl.pl b/repl.pl
new file mode 100644
index 0000000..eb272a9
--- /dev/null
+++ b/repl.pl
@@ -0,0 +1,77 @@
+:- module(repl, []).
+
+repl :-
+	catch(read_eval_print, E, print_exception(E)),
+	'$collect_garbage',
+	repl.
+
+read_eval_print :-
+	write('?- '),
+	asserta(found_a_solution :- (!, fail)),
+	read_term(Term, [variable_names(Vars)]),
+	'$choicestack_size'(Choicecount),
+	eval_and_print(Term, Vars, Choicecount),
+	!,
+	abolish(found_a_solution/0).
+
+eval_and_print(Goal, Vars, Choicecount) :-
+	user:call(Goal),
+	abolish(found_a_solution/0),
+	asserta(found_a_solution :- !),
+	'$choicestack_size'(ChoicecountNew),
+	( ChoicecountNew > Choicecount + 1
+	-> write_result(Vars, more),
+	   get_raw_char(Char),
+	   ( Char = ';'
+	   -> put_char(Char),
+	      nl,
+	      '$collect_garbage',
+	      asserta(found_a_solution :- (!, fail)),
+              fail % backtrack and call G again
+	   ; put_char('.'), nl
+	   )
+	; write_result(Vars, end)
+	).
+eval_and_print(Goal, _, _) :-
+	\+ found_a_solution,
+	write('false.'),
+	nl.
+
+write_state(end) :- write('.'), nl.
+write_state(more).
+
+write_result([], State) :- write('true'), write_state(State).
+write_result([B|Bs], State) :- write_bindings([B|Bs]), write_state(State).
+
+write_bindings([]).
+write_bindings([B|Bs]) :-
+	write(B),
+	( Bs = []
+	-> true
+	; put_char(','), nl
+	),
+	write_bindings(Bs).
+
+print_exception(E) :-
+	write('Unhandled exception: '),
+	write(E),
+	nl.
+
+whitespace(' ').
+whitespace('	').
+whitespace('
+').
+
+get_raw_char(Char) :-
+	open('/dev/consctl', write, S),
+	write(S, rawon),
+	get_one_char(Char),
+	write(S, rawoff),
+	close(S).
+
+get_one_char(Char) :-
+	get_char(C),
+	( whitespace(C)
+	-> get_one_char(Char)
+	; Char = C
+	).
-- 
cgit v1.2.3