24 lines
511 B
Plaintext
24 lines
511 B
Plaintext
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:- object(calculator,
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implements(parsep)).
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parse(Expression, Value) :-
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phrase(expr(Value), Expression).
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expr(Z) --> term(X), "+", expr(Y), {Z is X + Y}.
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expr(Z) --> term(X), "-", expr(Y), {Z is X - Y}.
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expr(X) --> term(X).
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term(Z) --> number(X), "*", term(Y), {Z is X * Y}.
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term(Z) --> number(X), "/", term(Y), {Z is X / Y}.
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term(Z) --> number(Z).
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number(C) --> "+", number(C).
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number(C) --> "-", number(X), {C is -X}.
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number(X) --> [C], {0'0 =< C, C =< 0'9, X is C - 0'0}.
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:- end_object.
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