isDigit

Selects ASCII digits, i.e. '0'..'9'.
A fast digit predicate.
Is this an ASCII digit, i.e., one of 0..9. Note that this is a subset of isNumberL1.
>>> prove $ \c -> isDigit c .=> isNumberL1 c
Q.E.D.
isDigit c = '0' <= c && c <= '9'
Decimal digit predicate.
A fast digit predicate.
Test if a character is a digit.
Determines whether a character is numeric (i.e. a digit). This covers ASCII 0-9 and also digits in other languages/scripts. Given some UTF-8 text, obtain a character value with utf8GetChar.