Result is cos(Number)
which should be preferred for portability.
In coroutining mode, if Number is uninstantiated, the call to cos/2 is delayed until this variable is instantiated.
Success:
cos(0, 1.0).
cos(1.2, Result). (gives Result = 0.362358)
cos(-33, Result). (gives Result = -0.0132767)
Fail:
cos(1, 0.0).
cos(0, 1).
cos(5, r).
Error:
cos(A, 6.0). (Error 4).
cos(4 + 2, 0.96017). (Error 24).