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