is there any difference between the two types "a" and "t" in Haskell type signature or its only a different designation like type "a" and type "b"?
in https://www.haskell.org/tutorial/goodies.html type [a] is defined as followed:
[a] is the family of types consisting of, for every type a, the type of lists of a. Lists of integers (e.g. [1,2,3]), lists of characters (['a','b','c']), even lists of lists of integers, etc., are all members of this family. (Note, however, that [2,'b'] is not a valid example, since there is no single type that contains both 2 and 'b'.)
is this definition also applied for type "t" ?
an example might be :
foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b
app :: [t] -> t -> [t]