31 lines
715 B
Prolog
31 lines
715 B
Prolog
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% Compute the nth number in the fibonacci sequence
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fib(0, 0).
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fib(1, 1).
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fib(X, Res):-
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X1 is X - 1,
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X2 is X - 2,
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fib(X1, Tmp1),
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fib(X2, Tmp2),
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Res is Tmp1 + Tmp2.
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% Compute the nth element of the integer factorial
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fac(0, 1).
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fac(X, Res):-
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X1 is X - 1,
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fac(X1, Tmp),
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Res is Tmp * X.
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% Sums all integer numbers between and inclusive X and inclusive Y and writes the result to Res.
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%
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% example: sum(0, 9, X).
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% output: X = 45
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% explanation: 0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 9
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sum(X, X, X).
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sum(X, Y, Res):-
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X < Y,
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X1 is X + 1,
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sum(X1, Y, Tmp),
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Res is Tmp + X.
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sum(X, Y, Res):- % if X is bigger than Y, swap the operands and call sum again
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X > Y,
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sum(Y, X, Res).
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