make character predicates (isspace etc) work for strings arguments too

[stevengj]

This adds the simple convenience that functions like isspace or isalpha can work for string arguments as well as for individual characters (returning true for a string if the predicate is true for all characters in the string).

[StefanKarpinski]

Seems reasonable to me although the fact that all predicates are true for "" seems potentially problematic. Perhaps they should only return true for non-empty strings where all the characters satisfy the predicate. It's easy enough to explicitly write isempty(s) || isdigit(s) if you actually wanted to allow the empty string.

[johnmyleswhite]

+1

[stevengj]

Is this string all of this character type? should be true for an empty string.

For example, I would tend to want isspace("") to be true, and returning true for the empty string is a nice, comprehensible semantic meaning if applied uniformly to all isfoo functions. It is also conceptually consistent with the general concept of an empty product of logical ands (as well as with our all function).

It is easy enough to write !isempty(s) && isdigit(s) if you want to exclude the empty string.