[Agda] Problem with generalised variables

[Thorsten Altenkirch]

Hi,

I am writing some material about combinators and thought it is quite nice to use generalized variables for types:

variable
  A B C : Set

K : A → B → A
K x y = x

S : (A → B → C) → (A → B) → (A → C)
S f g x = f x (g x)

However, when I try to define

I : A → A
I = S K K

I run into the usual problem of an uninstantiated metavariable. Using explicit abstraction I was able to fix this by saying

I : A → A
I = S K (K {B = A})

But when I try this in this setting I get quite a mouthy error message.

Any advice? I don’t really want to introduce fake modules of possible because then I would to indent everything.

Thorsten





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