Proposal: Make digitToInt and intToDigit work up to base 36

[Twan van Laarhoven]

Hello List,


I propose to change the functions digitToInt and intToDigit in Data.Char to

digitToInt :: Char -> Int
digitToInt c
   | isDigit c            =  ord c - ord '0'
   | c >= 'a' && c <= 'z' =  ord c - ord 'a' + 10
   | c >= 'A' && c <= 'Z' =  ord c - ord 'A' + 10
   | otherwise            =  error ("Char.digitToInt: not a digit " ++ show c)

intToDigit :: Int -> Char
intToDigit i
   | i >= 0  && i <=  9   =  toEnum (fromEnum '0' + i)
   | i >= 10 && i <= 35   =  toEnum (fromEnum 'a' + i - 10)
   | otherwise            =  error "Char.intToDigit: not a digit"

(and equivalently for the Ghc specialized version in Data.Show)

Right now the functions only work for c <= 'f' and i <= 15, i.e. only up to 
hexadecimal. But I can think of no reason why that should be the case.

There is the problem of compatibility with the Haskell98/2010 report. But since 
this proposed change only reduces the number of cases that are errors, I think 
that is not a big concern.


Discussion period: 2 weeks, deadline July 13.


Twan