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# sgn(+Number, -Result)

Unifies Result with the sign of Number which is either -1, 0 or 1.

Number
  A number.
Result
  A variable or an integer.

## Description

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

- sgn(+, -) is det

### Exceptions

(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.

## Examples

    Success:
          sgn(42, 1).
          sgn(-5, Result).             (gives Result = -1)
          sgn(-6.2, Result).           (gives Result = -1)
          sgn(0.0, 0).
    Fail:
          sgn(1, 0).
    Error:
          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