Data commit

Task/Balanced-brackets/Mercury/balanced-brackets.mercury

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+:- module balancedbrackets.
+:- interface.
+
+:- import_module io.
+
+:- pred main(io::di, io::uo) is det.
+
+
+:- import_module list, random, char.
+
+:- pred brackets(int::in,list(char)::out,supply::mdi,supply::muo) is det.
+
+:- pred imbalance(list(char)::in,int::out) is semidet.
+:- pred balanced(list(char)::in) is semidet.
+
+:- implementation.
+
+:- import_module int.
+
+imbalance([],0).
+imbalance(['['|T],N) :- imbalance(T,N+1).
+imbalance([']'|T],N) :- N > 0, imbalance(T,N-1).
+
+balanced(S) :- imbalance(S,0).
+
+brackets(N,S,!RS) :-
+    (
+	N < 1 -> S is []
+    ;   random(0,2,R,!RS),
+	( R is 0 -> S is ['['|T], brackets(N-1,T,!RS)
+	; S is [']'|T], brackets(N-1,T,!RS))).
+
+main(!IO) :-
+    random.init(0,RS),
+    brackets(4,S,RS,_),
+    print(S,!IO),
+    (
+	balanced(S) -> print(" is balanced\n",!IO)
+    ;   print(" is unbalanced\n", !IO)
+    ).