Hi Angus,
Your understanding is correct. Parenthesis is need in a -> a to specify
that it is function from a to a because associativity of -> is from right
to left. (*2) is section, you can read more
about here :
http://www.haskell.org/haskellwiki/Section_of_an_infix_operator.
Type of (*2) is (Num a) :: a -> a rather than particular type Int.
Thanks
Divyanshu Ranjan
On Tue, Dec 31, 2013 at 8:16 PM, Angus Comber
iterate' :: (a -> a) -> a -> [a]
I am trying going to go ahead and write my own iterate function. But before I do I want to be clear on types.
Looking at :: (a -> a) -> a -> [a]
The first part is (a -> a) Now because it is in parentheses it is a function?
I can call iterate like this: take 5 $ iterate (*2) 5
So (*2) is a possible function. Does the brackets mean it is a function, the left hand a is indicating a general type and the right hand a means the return type must be the same as the function type. Eg in the case of (*2) the 2 is an Int so the function returns and Int? Is my understanding correct?
How could this be better explained?
The last bit is easier to understand. a -> [a] meaning a singleton of general type and [a] means a list of same type.
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