Re: read "hexadecimal digits"?

Malcolm Wallace <[email protected]> Mon, 31 May 2004 11:19:14 +0100

Newsgroups	gmane.comp.lang.haskell.nhc.bugs
Organization	Dept of Computer Science, University of York
Message-ID	<[email protected]>

Kwanghoon Choi <[email protected]> writes:

> As the following script shows, hexa-decimal digits
> cannot be recognized by 'Prelude.read'. 
> It seems to be a bug.
>     main =  putStrLn (show (chr (read "0x2B" :: Int)))

Actually, it is conformant Haskell'98 behaviour.  The Prelude defines

    instance Read Int where
        readsPrec p = readSigned readDec

(or a very near equivalent), that is, it uses readDec for decimal
notation, rather than using readOct or readHex for octal or hexadecimal
respectively.

Arguably, this is a bug in the Haskell'98 definition, but both nhc98
and Hugs follow the definition exactly in this case.

Regards,
    Malcolm