[Haskell-cafe] Introspection

[Sharadha Raghunathan]

Thanks. Let me try this. I appreciate all the help. And how do I compute a LR parser graph using haskell? 

Sent from my iPhone

On Jul 22, 2011, at 6:41 AM, Felipe Almeida Lessa <felipe.lessa at gmail.com> wrote:

> On Fri, Jul 22, 2011 at 10:31 AM, Stephen Tetley
> <stephen.tetley at gmail.com> wrote:
>> As Haskell is statically typed, if y.length < 100, y is still of type Big...
> 
> You could achieve this kind of thing with smart constructors and
> GADTs.  I don't know how useful it is, though =).
> 
> data Sized t a where
>  Small :: a -> Sized Small a
>  Big :: a -> Sized Big a
> 
> data Small -- empty
> data Big -- empty
> 
> retrieve :: Sized t a -> a
> retrieve (Small a) = a
> retrieve (Big a) = a
> 
> toSmall :: [a] -> Maybe (Sized Small [a])
> toSmall xs = if length xs < 100 then Just (Small xs) else Nothing
> 
> toBig :: ... -- almost the same as toSmall
> 
> toUnknown :: [a] -> (forall t. Sized t [a] -> r) -> r
> toUnknown xs f = if length xs < 100 then f (Small xs) else f (Big xs)
> 
> -- 
> Felipe.
> 
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