I'd urge you to *try* to maintain that safety throughout, but you can try something like this if necessary (I'm not at my computer, so I can't test it):

{-#LANGUAGE FlexibleContexts, FlexibleInstances #-}
instance Foldable (SL Z) where
  foldr _ n Nil = n

instance Foldable (SL n) => Foldable (SL (S n)) where
  foldr c n (Cons x xs) = c x (foldr c n xs)

In fact, I would expect whatever package you're looking at to offer this. Then you can just use Data.Foldable.toList.

On Mar 11, 2015 7:16 PM, "Sumit Sahrawat, Maths & Computing, IIT (BHU)" <sumit.sahrawat.apm13@iitbhu.ac.in> wrote:

The fixed-vector package uses a similar technique. The only trouble I'm having is with converting Vec v (Double, Double) to [(Double, Double)] for further use. I don't want to change all the code, but only the part where the user provides me with arguments.

I'll keep looking into it. Thanks for the help.

On 12 March 2015 at 04:44, David Feuer <david.feuer@gmail.com> wrote:

There are a lot of ways to do this sort of thing, and which one you choose will depend on exactly what you're trying to do. For example, you can write something vaguely like

data Nat = Z | S Nat
data SL (n :: Nat) a where
  Nil :: SL Z
  Cons :: a -> SL n a -> SL (S n) a

plot :: forall (n::Nat) . (SL n Double -> Double) ->
                                        SL n (Double, Double) -> IO ()

On Mar 11, 2015 5:45 PM, "Sumit Sahrawat, Maths & Computing, IIT (BHU)" <sumit.sahrawat.apm13@iitbhu.ac.in> wrote:

Hi everybody,

I have a function of type

    plot :: ([Double] -> Double)    -- A function to plot

         -> [(Double, Double)]      -- Range for all arguments

         -> IO ()

I want to enforce the fact that ranges for all arguments should be provided.

Is there a way to make the type system enforce it?

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Regards

Sumit Sahrawat

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Regards

Sumit Sahrawat