[Agda] Problem with generalised variables

[Thorsten Altenkirch]

Thank you, Guillaume.

I see the declaration 
I : A → A
Is just a shorthand for
I : {A : Set} → A → A

Hence if in the term I want to refer to A I have to introduce it as an explicit parameter.

Cheers,
Thorsten

On 23/07/2020, 17:31, "Guillaume Brunerie" <guillaume.brunerie at gmail.com> wrote:

    Hi Thorsten,

    I : A → A
    I {A} = S K (K {B = A})

    seems to work.

    Best,
    Guillaume

    Den tors 23 juli 2020 kl 18:04 skrev Thorsten Altenkirch
    <Thorsten.Altenkirch at nottingham.ac.uk>:
    >
    > 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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