From ab454375c090048b30e3863dd26f0d50f2e2f4f8 Mon Sep 17 00:00:00 2001
From: Simon Forman <sforman@hushmail.com>
Date: Sun, 11 Aug 2019 17:00:38 -0700
Subject: [PATCH] Clean up REPL formatting.

---
 thun/gnu-prolog/main.pl   |  8 ++++++--
 thun/gnu-prolog/parser.pl | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/thun/gnu-prolog/main.pl b/thun/gnu-prolog/main.pl
index 421dd2a..595bc57 100644
--- a/thun/gnu-prolog/main.pl
+++ b/thun/gnu-prolog/main.pl
@@ -22,12 +22,13 @@ Main Loop
 
 :- initialization(loop).
 
-loop :- line(Line), loop(Line, [], _Out).
+loop :- prompt, line(Line), loop(Line, [], _Out).
 
 loop([eof],  S,   S) :- !.
 loop( Line, In, Out) :-
   do_line(Line, In, S),
-  write(S), nl,
+  show_stack(S),
+  prompt,
   line(NextLine), !,
   loop(NextLine, S, Out).
 
@@ -35,3 +36,6 @@ loop( Line, In, Out) :-
 do_line(Line, In, Out) :- phrase(joy_parse(E), Line), thun(E, In, Out).
 do_line(_Line, S,   S) :- write('Err'), nl.
 
+prompt :- write(`joy? `).
+show_stack(S) :- nl, print_stack(S), write(` <-top`), nl, nl.
+
diff --git a/thun/gnu-prolog/parser.pl b/thun/gnu-prolog/parser.pl
index cd8a35c..4258f89 100644
--- a/thun/gnu-prolog/parser.pl
+++ b/thun/gnu-prolog/parser.pl
@@ -68,3 +68,40 @@ digits([]) --> [].
 
 digit(C) --> [C], { nonvar(C), C =< 57, C >= 48 }.
 
+
+/*
+
+Print state.
+
+*/
+
+format_state(Stack, Expression, Codes) :-
+    reverse(Stack, RStack),
+    phrase(format_joy(RStack), RStackCodes),
+    phrase(format_joy(Expression), ExpressionCodes),
+    append(RStackCodes, [32, 46, 32|ExpressionCodes], Codes).
+
+
+frump(Stack, Expression) :-
+    format_state(Stack, Expression, Codes),
+    maplist(put_code, Codes), nl.
+
+print_stack(Stack) :-
+    reverse(Stack, RStack),
+    phrase(format_joy(RStack), Codes),
+    maplist(put_code, Codes).
+
+
+
+% Print Joy expressions as text.
+
+format_joy(Tail)  --> {var(Tail)}, !, [46, 46, 46].
+format_joy([T])   --> format_term(T), !.
+format_joy([T|S]) --> format_term(T), " ", format_joy(S).
+format_joy([])    --> [].
+
+format_term(N) --> {number(N), number_codes(N, Codes)}, Codes.
+format_term(A) --> {  atom(A),   atom_codes(A, Codes)}, Codes.
+format_term([A|As]) --> "[", format_joy([A|As]), "]".
+
+