The iswctype function returns non-zero if and only if wc has the property described by charclass, or charclass is zero.
The wctype function returns 0 if property is invalid, otherwise it returns a value of type
.Vt wctype_t that can be used in subsequent calls to iswctype.
Reimplement iswalpha(3) in terms of iswctype and wctype:
return (iswctype(wc, wctype("alpha")));