If the arithmetic value of the argument is negative then -1 is returned, if the value is 0 then 0 is returned, else is 1 returned.
see also: arithmetic in Prolog
| Examples | |
| X is sign(-3.9). | succeeds, X is -1 |
| X is sign(0). | succeeds, X is 0 |
| X is sign(10.9). | succeeds, X is 1 |