I would like:

```
unknown_function(123.456) -> 456
unknown_function(1234.56) -> 56

```

Or

```
unknown_function(123.456) -> "456"

```

Is there a builtin for this? The builtin `trunc/1` does the opposite:

```
2> trunc(123.456).
123

```

There is this answer for C: [Extract decimal part from a floating point number in C](https://stackoverflow.com/questions/499939/extract-decimal-part-from-a-floating-point-number-in-c) and this for Java: [How to get the decimal part of a float?](https://stackoverflow.com/questions/5017072/how-to-get-the-decimal-part-of-a-float)