Haskel type declaration, function and tuple as arguments

Question

I'm doing a haskell assignment for school. I want to make a function called MapTuple, wich maps a function with a tuple as its arguments for an array of tuple. Im declaring it on the following way:

MapTuple :: [(a,b)] -> (a -> b) -> [b]

the way i want to use the function is as follows.

MapTuple :: [(Int, String)] -> (Int -> String) -> [String]

problem however is that I get the following error when compiling:

Invalid type signature: MapTuple :: ([(a, b)]) -> (a -> b) -> [b] Should be of form ::

What am I doing wrong?

Thanks a lot for helping me in advance!

Answer 1

Haskell has a naming convention that's actually part of the language

• Functions start with lower case
• Constructors start with upper case

So you need to change MapTuple to mapTuple

As for what a constructor is,

 data Foo = ThisIsAConstructor

It's basically a function that returns a Foo.