Is this correct?
[a] = a list with 1 single element
a = a list with as many elements as you want
Ps: I have some doubts because some functions are of type [a]->a
but also read, for example [2,3]
What is the difference between [a] and "a" in Haskhell?
3
asked by anonymous 07.10.2017 / 19:40
1 answer
3
Is not correct, when any function says func :: [a] -> a is telling us that it takes as a parameter any list (of any size) and returns an element of the same type from the list. The a variable can be of any type, if the list is of numbers then the result will be a number.
Let's look at an example:
The scope of the head function in Haskell ( :t head ):
head :: [a] -> a
head [1,2,3] -- 1
head [a,b,c] -- a
This function returns the first element of a list (head of the list). It can be a list of any size, just test to verify.
The tail function, which returns the tail of the list, has a slightly different scope:
tail :: [a] -> [a]
tail [1,2,3] -- [2,3]
tail [a,b,c] -- [b,c]
Since the tail can have 0 or more elements.
If it were an Equals type function it would look something like this:
eq :: a -> a -> Bool
That is, it gets two parameters of the same type and returns true / false. To learn more about Haskell I recommend this book online .
07.10.2017 / 21:02