Parsec issue

[Christian Maeder]

Your observations are correct. The documentation at
http://legacy.cs.uu.nl/daan/parsec.html would need to be updated by Daan
(which will not happen, I'm afraid). Parsec's haddock documentation is poor.

I would recommend not to use Text.ParserCombinators.Parsec.Token and
Text.ParserCombinators.Parsec.Language for your own language, but only
take out those bits from the sources that you need for your language and
remain "portable".

Cheers Christian

Lennart Kolmodin wrote:
> Hi dear list,
> 
> while using parsec for a project I ran into this issue. Take the following
> program:
> 
> import Text.ParserCombinators.Parsec
> import Text.ParserCombinators.Parsec.Language
> import Text.ParserCombinators.Parsec.Token
> 
> main = do
>     run "0xf"
>     run "xf"
> 
> run str = putStrLn $ str ++ " parses as: " ++ show (parse p "" str)
> 
> p = hexadecimal $ makeTokenParser emptyDef
> 
> -----
> 
> Running it yields:
> 
> 0xf parses as: Left (line 1, column 1):
> unexpected "0"
> xf parses as: Right 15
> 
> -----
> 
> Looking at the code for hexadecimal in Parsec.Token it looks like:
>     hexadecimal     = do{ oneOf "xX"; number 16 hexDigit }
> clearly not handling the leading zero as the docs states:
> 
> hexadecimal  :: CharParser st Integer
> Parses a positive whole number in the hexadecimal system. The number
> should be prefixed with "0x" or "0X". Returns the value of the number.
> 
> Same goes for 'octal' in the same module.
> 
> Parsing using 'natural' works though:
> 
> nat             = zeroNumber <|> decimal
> 
> zeroNumber      = do{ char '0'
>                     ; hexadecimal <|> octal <|> decimal <|> return 0
>                     }
> 
> Also, neither hexadecimal nor octal eat the trailing whitespaces as
> natural, integer and float does (using lexme).
> 
> Am I missing something?
> 
> Cheers,
>   Lennart K