ensuringArgumentIsVarOrCharCode
fun <C : ExecutionContext> Solve.Request<C>.ensuringArgumentIsVarOrCharCode(index: Int): Solve.Request<C>
Ensures the argument at index is either unbound, -1 (end-of-file), or a valid character code, as required by the "code" argument of get_code/1,2 and peek_code/1,2.
Throws
(character_code) if it is an Integer outside the representable character-code range.