swipl 5.6.xVersion of implementation SWI-Prolog of programming language Prolog
A version of SWI-Prolog compiler.
This example doesn’t need any facts or rules to be evaluated. The query is executed in interactive mode, and results in the following output:
First line is the actual output of
write predicate, and second line is the result of query evaluation.
Note that replacing single-quotes with double-quotes makes Prolog output the string as an array of ASCII-codes of individual characters:
| ?- write("Hello, World!").
write('Hello, World!'), nl.
This is an ISO Prolog example, using standard read/1 predicate for reading input. Note that when using read/1, you have to put full stop . after each value you input.
q :- write('A = '), read(A), ( A = 0, write('Not a quadratic equation'); write('B = '), read(B), write('C = '), read(C), D is B*B-4*A*C, ( D = 0, write('x = '), X is -B/2/A, write(X); D > 0, write('x1 = '), X1 is (-B+sqrt(D))/2/A, write(X1), nl, write('x2 = '), X2 is (-B-sqrt(D))/2/A, write(X2); R is -B/2/A, I is abs(sqrt(-D)/2/A), write('x1 = ('), write(R), write(', '), write(I), write(')'), nl, write('x1 = ('), write(R), write(', -'), write(I), write(')') ) ).
Almost identical to Poplog Prolog example, except for the syntax of compiling a file (doesn’t have a
- before file name). However, the results of execution depend on the implementation. SWI-Prolog handles large numbers just fine, while in GNU Prolog and B-Prolog 12! overflows the numeric data type, so all values after 11! are incorrect.
| ?- [fact].
compiling /home/nickolas/Desktop/progopedia/prolog/fact.pl for byte code…
/home/nickolas/Desktop/progopedia/prolog/fact.pl compiled, 3 lines read — 1372 bytes written, 5 ms
| ?- fact(16,X).
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
10! = 3628800
11! = 39916800
12! = -57869312
13! = -215430144
14! = 205203456
15! = -143173632
16! = -143294464
X = -143294464 ?`
% fact.pl fact(X, F) :- ( X=0, F=1; Y is X-1, fact(Y, Z), F is X*Z), write(X), write('! = '), write(F), nl. % interactive [fact]. fact(16,X).
Once again, the example is almost identical to Poplog Prolog one, except for the syntax of compiling/consulting a file.
% fibonacci.pl :- dynamic(stored/1). memo(Goal) :- stored(Goal) -> true; Goal, assertz(stored(Goal)). fib(1,1) :- !, write('1, '). fib(2,1) :- !, write('1, '). fib(N,F) :- N1 is N-1, memo(fib(N1,F1)), N2 is N-2, memo(fib(N2,F2)), F is F1 + F2, write(F), write(', '). % interactive [fibonacci]. fib(16,X), write('...'), nl.