added .moo (parser definitions) to Mercury extension list

samples/Mercury/expr.moo

@@ -0,0 +1,72 @@
+:- module expr.
+
+:- interface.
+
+:- import_module char, int, list.
+
+:- type token
+	--->	('+')
+	;	('-')
+	;	('*')
+	;	('/')
+	;	num(int)
+	;	('(')
+	;	(')')
+	;	eof
+	.
+
+:- parse(exprn/1, token, eof, xx, in, out).
+
+:- pred scan(list(char), list(token)).
+:- mode scan(in, out) is det.
+
+:- implementation.
+
+:- import_module string, require.
+
+:- rule exprn(int).
+exprn(Num)	--->	exprn(A), [+], term(B), { Num = A + B }.
+exprn(Num)	--->	exprn(A), [-], term(B), { Num = A - B }.
+exprn(Num)	--->	term(Num).
+
+:- rule term(int).
+term(Num)	--->	term(A), [*], factor(B), { Num = A * B }.
+term(Num)	--->	term(A), [/], factor(B), { Num = A // B }.
+term(Num)	--->	factor(Num).
+
+:- rule factor(int).
+factor(Num)	--->	['('], exprn(Num), [')'].
+factor(Num)	--->	[num(Num)].
+
+scan(Chars, Toks) :-
+	scan(Chars, [], Toks0),
+	list__reverse(Toks0, Toks).
+
+:- pred scan(list(char), list(token), list(token)).
+:- mode scan(in, in, out) is det.
+
+scan([], Toks, [eof|Toks]).
+scan([C|Cs], Toks0, Toks) :-
+	( char__is_whitespace(C) ->
+		scan(Cs, Toks0, Toks)
+	; char__is_digit(C) ->
+		takewhile(char__is_digit, [C|Cs], Digits, Rest),
+		string__from_char_list(Digits, NumStr),
+		Num = string__det_to_int(NumStr),
+		scan(Rest, [num(Num)|Toks0], Toks)
+	; C = ('+') ->
+		scan(Cs, ['+'|Toks0], Toks)
+	; C = ('-') ->
+		scan(Cs, ['-'|Toks0], Toks)
+	; C = ('*') ->
+		scan(Cs, ['*'|Toks0], Toks)
+	; C = ('/') ->
+		scan(Cs, ['/'|Toks0], Toks)
+	; C = ('(') ->
+		scan(Cs, ['('|Toks0], Toks)
+	; C = (')') ->
+		scan(Cs, [')'|Toks0], Toks)
+	;
+		error("expr: syntax error in input")
+	).
+