genericIndex is:exact

The genericIndex function is an overloaded version of !!, which accepts any Integral value as the index.
Like index, except with a more general Integral argument
Like index, except with a more general Integral argument Pre-release
Index a string at any location Just like the other generic functions of this module, this function can be significantly slower than index, since the function must be able to support arbitrarily large indices. Consider using index or index64, even if you need to coerce the index to an Int.