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sgn(+Number, -Result)

Unifies Result with the sign of Number which is either -1, 0 or 1.
A number.
A variable or an integer.


This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to sgn(Number, Result) is equivalent to
    Result is sgn(Number)
which should be preferred for portability.

sgn/2 gives the integer -1 if Number is negative, 0 if it is zero and 1 if it is greater than zero. It is always true that

    X =:= sgn(X) * abs(X)
In coroutining mode, if Number is uninstantiated, the call to sgn/2 is delayed until this variable is instantiated.

Modes and Determinism


(4) instantiation fault
Number is not instantiated (non-coroutining mode only).
(5) type error
Result is a non-integer number.
(24) number expected
Number is not of a numeric type.
(24) number expected
Result is neither a number nor a variable.


      sgn(42, 1).
      sgn(-5, Result).             (gives Result = -1)
      sgn(-6.2, Result).           (gives Result = -1)
      sgn(0.0, 0).
      sgn(1, 0).
      sgn(A, 6).                   (Error 4).
      sgn(1, 1.0).                 (Error 5).
      sgn(4 + 2, 6).               (Error 24).
      sgn(1, r).                   (Error 24).

See Also

is / 2