Balanced brackets: Difference between revisions

=={{header|Mercury}}==

<lang Mercury>

:- 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)

).

</lang>