diff --git a/thun/gnu-prolog/parser.pl b/thun/gnu-prolog/parser.pl
index f25d5d0..c953d03 100644
--- a/thun/gnu-prolog/parser.pl
+++ b/thun/gnu-prolog/parser.pl
@@ -33,6 +33,28 @@ joy_term(C) --> symbol(C).
 symbol(C) --> chars(Chars), !, {Chars \= "==", atom_codes(C, Chars)}.
 
 
+% TODO: negative numbers, floats, scientific notation.
+
+num(N) --> digits(Codes), !, { number_codes(N, Codes) }.
+
+% Groups of characters.
+
+chars([Ch|Rest]) --> char(Ch), chars(Rest).
+chars([Ch])      --> char(Ch).
+
+blanks --> blank, !, blanks.
+blanks --> [].
+
+digits([Ch|Rest]) --> digit(Ch), digits(Rest).
+digits([Ch])      --> digit(Ch).
+
+% Character types.
+
+char(Ch)  --> [Ch], { nonvar(Ch), Ch \== 0'[, Ch \== 0'], between(33, 126, Ch) }.
+blank     --> [Ch], { nonvar(Ch), Ch =:= 32 ; between(9, 13, Ch) }.
+digit(Ch) --> [Ch], { nonvar(Ch), between(48, 57, Ch) }.
+
+
 % Line is the next new-line delimited line from standard input stream as
 % a list of character codes.
 
@@ -43,32 +65,6 @@ 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'], between(33, 126, Ch) }.
-
-
-blanks --> blank, !, blanks.
-blanks --> [].
-
-blank --> [Ch], { Ch =:= 32 ; between(9, 13, Ch) }.
-
-
-% 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), between(48, 57, C) }.
-
-
 /*
 
 Print state.