diff --git a/implementations/GNUProlog/Makefile b/implementations/GNUProlog/Makefile
new file mode 100644
index 0000000..2448c3c
--- /dev/null
+++ b/implementations/GNUProlog/Makefile
@@ -0,0 +1,12 @@
+
+all: joy_to_ast thun printer
+
+joy_to_ast: joy_to_ast.prolog
+	gplc --no-top-level joy_to_ast.prolog
+
+thun: thun.prolog
+	gplc --no-top-level thun.prolog
+
+printer: printer.prolog
+	gplc --no-top-level printer.prolog
+
diff --git a/implementations/GNUProlog/joy_to_ast.prolog b/implementations/GNUProlog/joy_to_ast.prolog
index 7219cc4..1a0fde3 100644
--- a/implementations/GNUProlog/joy_to_ast.prolog
+++ b/implementations/GNUProlog/joy_to_ast.prolog
@@ -1,5 +1,4 @@
 
-
 stdin_to_codes(Codes) :-
     % Pass in and discard atom 'code' to prime stdin_to_codes/2.
     stdin_to_codes(code, [code|Codes]).
@@ -9,6 +8,7 @@ stdin_to_codes(Code, [Code|Codes]) :-
     get_code(NextCode),
     stdin_to_codes(NextCode, Codes).
 
+
 %
 %joy(InputString, StackIn, StackOut) :-
 %    text_to_expression(InputString, Expression),
@@ -34,7 +34,7 @@ joy_parse([]) --> [].
 joy_term(list(J)) --> [lbracket], !, joy_parse(J), [rbracket].
 joy_term(Token) --> [tok(Codes)], {joy_token(Token, Codes)}.
 
-joy_token(int(I), Codes) :- catch(number_codes(I, Codes), _Err, fail), !.
+joy_token(int(I), Codes) :- numeric(Codes), atom_codes(I, Codes), !.
 joy_token(bool(true), "true") :- !.
 joy_token(bool(false), "false") :- !.
 joy_token(symbol(S), Codes) :- atom_codes(S, Codes).
@@ -51,6 +51,16 @@ chars([Ch])      --> char(Ch).
 
 char(Ch) --> \+ blank, [Ch], { Ch \== 0'[, Ch \== 0'] }.
 
+numeric(Codes) :- digits(Codes, []), !.
+numeric([45,FirstDigit|Codes]) :- digit(FirstDigit), digits(Codes, []), !.
+% ASCII 45 is '-'.
+
+digits --> digit, digits.
+digits --> [].
+
+digit --> [Code], { digit(Code) }.
+
+digit(Code) :- between(0'0, 0'9, Code).
 
 blank --> [9].
 blank --> [10].
@@ -82,5 +92,5 @@ blank --> [227, 128, 128].
 :- initialization((
     stdin_to_codes(Codes),
     text_to_expression(Codes, Expr),
-    print(Expr), print('\n')
-    )).
\ No newline at end of file
+    write_term(Expr, [quoted(true)]), print('\n')
+    )).
diff --git a/implementations/GNUProlog/printer.prolog b/implementations/GNUProlog/printer.prolog
new file mode 100644
index 0000000..c873ad0
--- /dev/null
+++ b/implementations/GNUProlog/printer.prolog
@@ -0,0 +1,25 @@
+
+format_joy_expression(   int(I)) --> { integer(I), !, number_codes(I, Codes) }, Codes.
+format_joy_expression(   int(I)) --> { atom(I), !, atom_codes(I, Codes) }, Codes.
+format_joy_expression(   int(I)) --> { write_to_codes(Codes, I) }, [40], Codes, [41].
+format_joy_expression(  bool(B)) --> { atom_codes(B, Codes) }, Codes.
+format_joy_expression(symbol(S)) --> { atom_codes(S, Codes) }, Codes.
+format_joy_expression(symbol(S)) --> { atom_codes(S, Codes) }, Codes.
+format_joy_expression(  list(J)) --> "[", format_joy_terms(J), "]".
+
+format_joy_terms(    []) --> [].
+format_joy_terms(   [T]) --> format_joy_expression(T), !.
+format_joy_terms([T|Ts]) --> format_joy_expression(T), " ", format_joy_terms(Ts).
+
+codes_to_stream([Code|Codes], Stream) :-
+    put_code(Stream, Code), !,
+    codes_to_stream(Codes, Stream).
+codes_to_stream([], _).
+
+:- initialization((
+    read_term(AST, [end_of_term(eof)]),
+    format_joy_terms(AST, Codes, []),
+    codes_to_stream(Codes, user_output), print('\n')
+    )).
+
+
diff --git a/implementations/GNUProlog/thun.prolog b/implementations/GNUProlog/thun.prolog
new file mode 100644
index 0000000..2f1dc17
--- /dev/null
+++ b/implementations/GNUProlog/thun.prolog
@@ -0,0 +1,73 @@
+
+
+thun([], S, S).
+thun([Term|E], Si, So) :- thun(Term, E, Si, So).
+
+thun(A,    [], S, [A|S]) :- var(A), !.
+thun(A, [T|E], S,   So)  :- var(A), !, thun(T, E, [A|S], So).
+
+thun(int(A),    [], B, [int(A)|B]).
+thun(int(C), [A|B], D, E) :- thun(A, B, [int(C)|D], E).
+
+thun(bool(A),    [], B, [bool(A)|B]).
+thun(bool(C), [A|B], D, E) :- thun(A, B, [bool(C)|D], E).
+
+thun(list(A),    [], B, [list(A)|B]).
+thun(list(C), [A|B], D, E) :- thun(A, B, [list(C)|D], E).
+
+thun(symbol(A),    [], B, C) :- func(A, B, C).
+thun(symbol(A), [C|D], B, F) :- func(A, B, E), thun(C, D, E, F).
+
+thun(symbol(Combo), E, Si, So) :- combo(Combo, Si, S, E, Eo), thun(Eo, S, So).
+
+
+func(swap, [A, B|S],  [B, A|S]).
+func(dup,     [A|S],  [A, A|S]).
+func(pop,     [_|S],        S ).
+
+func(cons,   [list(A),      B |S], [list([B|A])|S]).
+
+func(swaack,    [list(R)|S],   [list(S)|R]).
+func(stack,              S ,   [list(S)|S]).
+func(clear,              _ ,            []).
+func(first, [list([X|_])|S],   [     X |S]).
+func(rest,  [list([_|X])|S],   [list(X)|S]).
+
+func(bool, [     int(0)|S], [bool(false)|S]).
+func(bool, [   list([])|S], [bool(false)|S]).
+func(bool, [bool(false)|S], [bool(false)|S]).
+
+func(bool, [     int(N)|S], [bool(true)|S]) :- N #\= 0.
+func(bool, [list([_|_])|S], [bool(true)|S]).
+func(bool, [ bool(true)|S], [bool(true)|S]).
+
+func( + ,  [int(A), int(B)|S], [int(A + B)|S]).
+func( - ,  [int(A), int(B)|S], [int(B - A)|S]).
+func( * ,  [int(A), int(B)|S], [int(A * B)|S]).
+func( / ,  [int(A), int(B)|S], [int(B div A)|S]).
+func('%',  [int(A), int(B)|S], [int(B mod A)|S]).
+
+func( add ,  [int(A), int(B)|S], [int(A + B)|S]).
+func( sub ,  [int(A), int(B)|S], [int(B - A)|S]).
+func( mul ,  [int(A), int(B)|S], [int(A * B)|S]).
+func( div ,  [int(A), int(B)|S], [int(B div A)|S]).
+func( mod,  [int(A), int(B)|S], [int(B mod A)|S]).
+
+
+combo(i,          [list(P)|S], S, Ei, Eo) :- append(P, Ei, Eo).
+combo(dip,     [list(P), X|S], S, Ei, Eo) :- append(P, [X|Ei], Eo).
+
+combo(branch, [list(T), list(_),  bool(true)|S], S, Ei, Eo) :- append(T, Ei, Eo).
+combo(branch, [list(_), list(F), bool(false)|S], S, Ei, Eo) :- append(F, Ei, Eo).
+
+combo(loop, [list(_), bool(false)|S], S, E,  E ).
+combo(loop, [list(B),  bool(true)|S], S, Ei, Eo) :- append(B, [list(B), symbol(loop)|Ei], Eo).
+
+
+
+:- initialization((
+    read_term(AST, [end_of_term(eof)]),
+    thun(AST, [], Stack),
+    write_term(Stack, [quoted(true)]), print('\n')
+    )).
+