I'm going through "Haskell Programming from first principles" and in section 7.3 Anonymous Functions there is an exercise on converting multiple parameters to anonymous functions, and it asks:
1. Which (two or more) of the following are equivalent?
mTh1 x y z = x * y * z
mTh2 x y = \z -> x * y * z
mTh3 x = \y -> \z -> x * y * z
mTh4 = \x -> \y -> \z -> x * y * z
So I created a file, anon.hs (attached):
module Anon where
mTh1 x y z = x * y * z
mTh2 x y = \z -> x * y * z
mTh3 x = \y -> \z -> x * y * z
mTh4 = \x -> \y -> \z -> x * y * z
I load that into ghci and check the function types:
$ ghci anon.hs
[1 of 1] Compiling Anon ( anon.hs, interpreted )
Ok, 1 module loaded.
*Anon> :t mTh1
mTh1 :: Num a => a -> a -> a -> a
*Anon> :t mTh2
mTh2 :: Num a => a -> a -> a -> a
*Anon> :t mTh3
mTh3 :: Num a => a -> a -> a -> a
*Anon> :t mTh4
mTh4 :: Integer -> Integer -> Integer -> Integer
Why is mTh4 different from the rest?
On the flip side If I enter "mTh4 = \x -> \y -> \z -> x * y * z" directly in ghci command line then it has same type as the others:
$ ghci
Prelude> mTh4 = \x -> \y -> \z -> x * y * z
Prelude> :t mTh4
mTh4 :: Num a => a -> a -> a -> a
-- Wink