Re: [Haskell-cafe] Re: Write Haskell as fast as C.

Andrew Coppin wrote: [...]

I think you'll find the code that GHC derives for a Read instance handles extra whitespace and all kinds of other whatnot that you don't actually need in this specific case. I suspect this is what's up - but I don't have any hard proof for that. ;-)

Parentheses are handled as well. It's worse than that - derived read instances are defined in terms of 'lex' (via lexP in GHC.Read) which, among other things, recognizes numerical and string constants. The latter has the odd effect that with the following declaration,

data A = A deriving (Read, Show)

the expression read ('"' : repeat ' ') :: A is the wrong kind of bottom - instead of a parse error, you get an infinite loop. Bertram