A function.
| arg | An instance of <string>. |
| start: | An instance of <integer>. The default is 0. |
| default: | An instance of <object>. The default is $not-supplied. |
| end: | An instance of type-union(<integer>, <false>). The default is #f. |
| val | An instance of <machine-word>. |
| val | An instance of <integer>. |