diff --git a/thun/gnu-prolog/Makefile b/thun/gnu-prolog/Makefile
index 3031b1d..abb7905 100644
--- a/thun/gnu-prolog/Makefile
+++ b/thun/gnu-prolog/Makefile
@@ -1,7 +1,7 @@
 GPLC_OPTIONS="--min-size"
 
-thun: thun.pl
-	gplc $(GPLC_OPTIONS) -o thun thun.pl
+thun: thun.pl parser.pl
+	gplc $(GPLC_OPTIONS) -o thun thun.pl parser.pl
 
 defs.pl: meta-defs.pl defs.txt
 	gprolog --consult-file meta-defs.pl defs.txt
diff --git a/thun/gnu-prolog/parser.pl b/thun/gnu-prolog/parser.pl
new file mode 100644
index 0000000..7787a7a
--- /dev/null
+++ b/thun/gnu-prolog/parser.pl
@@ -0,0 +1,72 @@
+/*
+    Copyright  2018, 2019 Simon Forman
+
+    This file is part of Thun
+
+    Thun is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Thun is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Thun.  If not see <http://www.gnu.org/licenses/>.
+
+
+Parser
+
+*/
+
+:- set_prolog_flag(double_quotes, codes).
+
+joy_parse([T|J]) --> blanks, joy_term(T), blanks, joy_parse(J).
+joy_parse([]) --> [].
+
+joy_term(N) --> num(N), !.
+joy_term(J) --> "[", !, joy_parse(J), "]".
+joy_term(C) --> symbol(C).
+
+symbol(C) --> chars(Chars), !, {Chars \= [61, 61], atom_codes(C, Chars)}.
+
+
+
+% Line is the next new-line delimited line from standard input stream as
+% a list of character codes.
+
+line(Line) :- get_code(X), line(X, Line).
+
+line(10,      []) :- !.  % break on new-lines.
+line(-1,   [eof]) :- !.  % break on EOF
+line(X, [X|Line]) :- get_code(Y), !, line(Y, Line).
+
+
+chars([Ch|Rest]) --> char(Ch), chars(Rest).
+chars([Ch])      --> char(Ch).
+
+char(Ch) --> [Ch], { Ch \== 0'[, Ch \== 0'], Ch >= 33, Ch =< 126 }.
+
+
+blanks --> blank, !, blanks.
+blanks --> [].
+
+blank --> [32].
+
+
+% TODO: negative numbers, floats, scientific notation.
+
+num(N) --> digits(Codes), !, { num(N, Codes) }.
+
+num(_, []) :- fail, !.
+num(N, [C|Codes]) :- number_codes(N, [C|Codes]).
+
+
+digits([H|T]) --> digit(H), !, digits(T).
+digits([]) --> [].
+
+digit(C) --> [C], { nonvar(C), C =< 57, C >= 48 }.
+
+
diff --git a/thun/gnu-prolog/thun.pl b/thun/gnu-prolog/thun.pl
index 61060ca..52d80c0 100644
--- a/thun/gnu-prolog/thun.pl
+++ b/thun/gnu-prolog/thun.pl
@@ -205,17 +205,6 @@ Definitions
 def(x, [dup, i]).
 
 
-/*
-Parser
-*/
-
-joy_parse([T|S]) --> blanks, joy_term(T), blanks, joy_parse(S).
-joy_parse([]) --> [].
-
-joy_term(N) --> num(N), !.
-joy_term(S) --> [0'[], !, joy_parse(S), [0']].
-joy_term(A) --> chars(Chars), !, {atom_codes(A, Chars)}.
-
 
 /*
 Main Loop
@@ -236,39 +225,3 @@ do_line(_Line, S,   S) :- write('Err'), nl.
 
 
 
-% Line is the next new-line delimited line from standard input stream as
-% a list of character codes.
-
-line(Line) :- get_code(X), line(X, Line).
-
-line(10,      []) :- !.  % break on new-lines.
-line(-1,   [eof]) :- !.  % break on EOF
-line(X, [X|Line]) :- get_code(Y), !, line(Y, Line).
-
-
-chars([Ch|Rest]) --> char(Ch), chars(Rest).
-chars([Ch])      --> char(Ch).
-
-char(Ch) --> [Ch], { Ch \== 0'[, Ch \== 0'], Ch >= 33, Ch =< 126 }.
-
-
-blanks --> blank, !, blanks.
-blanks --> [].
-
-blank --> [32].
-
-
-% TODO: negative numbers, floats, scientific notation.
-
-num(N) --> digits(Codes), !, { num(N, Codes) }.
-
-num(_, []) :- fail, !.
-num(N, [C|Codes]) :- number_codes(N, [C|Codes]).
-
-
-digits([H|T]) --> digit(H), !, digits(T).
-digits([]) --> [].
-
-digit(C) --> [C], { nonvar(C), C =< 57, C >= 48 }.
-
-