Failure to derive Applicative-based type

[ron-wolf]

applyPure :: f (t1 -> t2) -> t1 -> f t2

-- applyPure cannot be realized.

applyPure :: Applicative f => f (t1 -> t2) -> t1 -> f t2

Error: Class not found: Applicative

It seems that Djinn does not support directly referencing the Applicative class (as well as other classes & types from Prelude) out-of-the box; instead, the class’s methods must be specified from scratch. Upon doing so for Applicative, the following correct result is produced:

applyPure :: (Applicative f) => f (t1 -> t2) -> t1 -> f t2
applyPure a b = a <*> pure b
-- or
applyPure a b = pure b *> (a <*> pure b)

Is there a possible way to import the Applicative class, or other relevant type definitions, rather than specifying them from scratch? I’m sure I must be missing something if I have to paste all of the following into Djinn in order to proceed:

class Applicative f where pure :: a -> f a; (<*>) :: f (a -> b) -> f a -> f b; liftA2 :: (a -> b -> c) -> f a -> f b -> f c; (*>) :: f a -> f b -> f b; (<*) :: f a -> f b -> f a; fmap :: (a -> b) -> f a -> f b; (<$) :: a -> f b -> f a; ($>) :: f a -> b -> f b; (<$>) :: (a -> b) -> f a -> f b; (<&>) :: f a -> (a -> b) -> f b; void :: f a -> f ()

[midirhee12]

I had a similar scenario with the following:

f ? (Num a, Num ((a -> Maybe b) -> Maybe b)) =>
     Maybe ((a -> Maybe b) -> Maybe b)

with the following error:
Error: Class not found: Num

I then tried a simple example:

foo ? Num a => a -> a -> a

And still the same error appears.

[jwaldmann]

Even if we could import these definitions, they would not work?

$ djinn 
Welcome to Djinn version 2011-07-23.
Type :h to get help.
Djinn> :verboseHelp
...
there is no instantiation of polymorphic functions, 
so classes where the methods are polymorphic do not work as expected.
...