I have found this online book to be fairly easy to understand
Take a look at the section called "The type of a function with more than one argument" and also follow the link to "Partial function application and currying"
If you decide to use this book, I would recommend reading the entire thing. I tried to skip around at first, but got lost pretty quickly. The author does a good job of adding complexity step by step, so it might be best to start from the beginning.
On Sun, Sep 27, 2009 at 3:22 AM, informationen
<informationen@gmx.de> wrote:
Hi,
i am trying to understand the Haskell type system. I thought i understood it
quite well until i encountered the three following exercises. As you can see, i
have the answers already. But i don't understand, why they are correct.
Could anybody tell me a good place where i could learn how to answers these kind
of questions correctly or could give me some explanations, why these answers are
correct?
Any help is highly appreciated.
Kind regards
Chris
Two functions f and g with the following signatures are given:
f :: a -> a
g :: b -> c -> b
A) Give the type of the following expressions:
1) g [False] True :: 2) g [] True :: 3) g (f True) :: 4) g f ::
Answers:
1 [Boolean] 2) [a] 3) c -> Bool
4) c -> (a -> a)1) g f 1
B) Which of the following statements is correct?
2) g (f 1) is type correct
3) g . (f 1) is type correct
4) g . f 1 is type correct
5) (g . f) 1 is type correct
6) none of the expressions is correct
Answers:
1,2 and 5 are correct.
C) A function h is given as: h p x = p (f x). Which of the following
statements is correct.
1) h :: a -> b -> a -> b
2) h :: (a -> a) -> a -> a
3) h :: (a -> b) -> a -> b
4) h is equivalent to h' with h' p = p . f
5) h is equivalent to h' with h' p = p f
5) h is equivalent to h' with h' p x = p f x
Answers:
(I am not sure, if i remember correctly, but 3) and 4) should be
correct.)
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