I'm playing with the haskell repo around a little.
why f2 behaves that way ? (I was expecting f2 takes only 1 argument), also what does t mean in the type?
BTW, why I have to prefix repo with let in order to define function?
λ> :t add -- f1
add :: Num a => a -> a
λ> let add n = (+) 1 -- f2 what does this mean?
λ> add 1 1
2
λ> :t add
add :: Num a => t -> a -> a
λ> add 1 3
4
add n = (+) 1
You never use n on the right hand side. Keep in mind that (+) 1 is short for \x -> (+) 1, and you'll see that
add n = (+) 1 = \x -> (+) 1 x
Or, equivalently
add n x = (+) 1 x
Therefore, n can be any type (here called t), since it is not used at all.
You meant
add n = (+) 1 n
BTW, why I have to prefix repo with let in order to define function?
Because you're using GHCi, which doesn't act the same as using GHC on a source file.
You are not using n, so it can be of any type you want. t is not some specific type, it means an argument of some type t.
A good indication that t is not used anywhere (and something is wrong) is the fact that only a has a Num constraint. So for add to work properly if it actually used t in the addition, it would have to somehow be able to add a to a variable of any type, including types that are not an instance of Num.
