[Haskell-beginners] Type depending on value

[Marcin Mrotek]

Hello,

In your function, the type `n`, and thus also the value of the
argument, would have to be known at compile time. I'm not sure if you
could make it to work. However, you can use the reflection package
(https://hackage.haskell.org/package/reflection) where you can find a
`reifyNat` function (
https://hackage.haskell.org/package/reflection-2.1.2/docs/Data-Reflection.html#g:1
) that lets you create a "temporary" type that never escapes the
callback you give to it, and so it doesn't have to be known at compile
time:

reifyNat :: forall r. Integer -> (forall n. KnownNat n => Proxy n -> r) -> r

The only requirement is that type `r` doesn't depend in any way on `n`
(but the computation itself can use it, it just has to return the same
type every time).

Best regards,
Marcin Mrotek