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

[Andrew Coppin]

Ketil Malde wrote:
> Ketil Malde <ketil at malde.org> writes:
>
>   
>>> data EvidenceCode = IAC | IUG | IFR | NAC | NR | ... deriving Show
>>>       
>
>   
>> Could it be that this derived read instance is somehow very inefficient?
>>     
>
> To answer my own question: this is exactly it, ghc derives less than
> optimal code in this case.  Rather than reiterate the case here, I did
> a quick writeup at http://blog.malde.org/, and would be quite happy
> about any feedback or suggestions.
>   

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. ;-)