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Task/Balanced-brackets/Prolog/balanced-brackets.pro

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+rosetta_brackets :-
+	test_brackets([]),
+	test_brackets(['[',']']),
+	test_brackets(['[',']','[',']']),
+	test_brackets(['[','[',']','[',']',']']),
+	test_brackets([']','[']),
+	test_brackets([']','[',']','[']),
+	test_brackets(['[',']',']','[','[',']']).
+
+balanced_brackets :-
+	gen_bracket(2,  B1, []), test_brackets(B1),
+	gen_bracket(4,  B2, []), test_brackets(B2),
+	gen_bracket(4,  B3, []), test_brackets(B3),
+	gen_bracket(6,  B4, []), test_brackets(B4),
+	gen_bracket(6,  B5, []), test_brackets(B5),
+	gen_bracket(8,  B6, []), test_brackets(B6),
+	gen_bracket(8,  B7, []), test_brackets(B7),
+	gen_bracket(10, B8, []), test_brackets(B8),
+	gen_bracket(10, B9, []), test_brackets(B9).
+
+test_brackets(Goal) :-
+	(   Goal = [] -> write('(empty)'); maplist(write, Goal)),
+	(   balanced_brackets(Goal, []) ->
+	    writeln(' succeed')
+	;
+	    writeln(' failed')
+	).
+
+% grammar of balanced brackets
+balanced_brackets --> [].
+
+balanced_brackets -->
+	['['],
+	balanced_brackets,
+	[']'].
+
+balanced_brackets -->
+	['[',']'],
+	balanced_brackets.
+
+
+% generator of random brackets
+gen_bracket(0) --> [].
+
+gen_bracket(N) -->
+	{N1 is N - 1,
+	 R is random(2)},
+	bracket(R),
+	gen_bracket(N1).
+
+bracket(0) --> ['['].
+bracket(1) --> [']'].