Sorry again fo the long break,

and thanks for explanation.

Three Questions:

1.) Because (->) is defined with itself, it is also a Meta Type Constructor (TYPE == variable Rank Type == a Meta Type ?)

2.) How do I define a function which takes a 3-Kinded Type:

let f:: h (g a); f a = a

where g * -> * and h (*->*)->*, but it did not work as:

h is deduced to be h * -> *.

Prelude> let f:: h (g a); f a = a

<interactive>:42:18: error:
    • Couldn't match type ‘h’ with ‘(->) (g a)’
      ‘h’ is a rigid type variable bound by
        the type signature for:
          f :: forall (h :: * -> *) (g :: * -> *) a. h (g a)
        at <interactive>:42:5-15
      Expected type: h (g a)
        Actual type: g a -> g a
    • The equation(s) for ‘f’ have one argument,
      but its type ‘h (g a)’ has none
    • Relevant bindings include
        f :: h (g a) (bound at <interactive>:42:18)

What can I do?

3.)
Is there any tool in Haskel where I can see which function parameter is bound to the given input, for instance something like a function showBinds:

showBinds const (\c -> "s") (\(b,c) -> "c")
Prelude> Param a gets (\c -> "s")
                           b gets (\(b,c) -> "c")

This is a simple example, but it gets more complicated with massive use of autocurrying.



 
On 11/25/2017 05:39 PM, Francesco Ariis wrote: