In coroutining mode, if Number is a free variable, the call to fix/2 is delayed until this variable is instantiated.
Success: fix(1.5, 1). fix(-6.4, -6). Fail: fix(1, 0). Error: fix(A, 6.0). (Error 4). fix(0.0, 0.0). (Error 5). fix(4 + 2.3, 6). (Error 24). fix(1, r). (Error 24).