digitToInt

Convert a single digit Char to the corresponding Int. This function fails unless its argument satisfies isHexDigit, but recognises both upper- and lower-case hexadecimal digits (that is, '0'..'9', 'a'..'f', 'A'..'F').

Examples

Characters '0' through '9' are converted properly to 0..9:

>>> map digitToInt ['0'..'9']
[0,1,2,3,4,5,6,7,8,9]

Both upper- and lower-case 'A' through 'F' are converted as well, to 10..15.

>>> map digitToInt ['a'..'f']
[10,11,12,13,14,15]

>>> map digitToInt ['A'..'F']
[10,11,12,13,14,15]

Anything else throws an exception:

>>> digitToInt 'G'
*** Exception: Char.digitToInt: not a digit 'G'

>>> digitToInt '♥'
*** Exception: Char.digitToInt: not a digit '\9829'

Return the decimal digit value of a decimal digit character. Such characters have the general category Nd (decimal digit numbers) and a NumericType_ of NTDecimal. No digit values are returned for any Han characters, because Han number characters are often used with a special Chinese-style number format (with characters for powers of 10 in between) instead of in decimal-positional notation. Unicode 4 explicitly assigns Han number characters a NumericType_ of NTNumeric instead of NTDecimal.

Convert a digit to an integer. Works for hexadecimal digits too. If the input isn't a digit, then return -1.

>>> prove $ \c -> isDigit c .|| isHexDigit c .=> digitToInt c .>= 0 .&& digitToInt c .<= 15
Q.E.D.

>>> prove $ \c -> sNot (isDigit c .|| isHexDigit c) .=> digitToInt c .== -1
Q.E.D.