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# +(+Number, -Result)

Checks if Number is a number and unifies it with Result.
*Number*
- A number.
*Result*
- A variable or a number.

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable
arithmetic expressions. So the call to +(Number, Result) is equivalent
to
Result is +Number

which should be preferred for portability.
Number and Result have to be of the same type.

In coroutining mode, if Number is uninstantiated, the call to +/2 is
delayed until this variable is instantiated.

### Modes and Determinism

### Exceptions

*(4) instantiation fault *
- Number is not instantiated (non-coroutining mode only).
*(24) number expected *
- Number is not of a numeric type.

## Examples

Success:
+(1, 1).
+(5, Result). (gives Result = 5)
+(-6.2, Result). (gives Result = -6.2)
Fail:
+(1, 0).
+(1.0, 1).
+(1, 1.0).
+(1, r).
Error:
+(A, 6). (Error 4).
+(4 + 2, 6). (Error 24).

## See Also

is / 2