CODEWITHSUNDEEP
listhaskellrecursion
EStudent
EStudent

Reputation: 15

Haskell creating a counter with a single input

I am a beginner and I want to define a function which shows how many elements are in one list. I already created this :

elementsl n []     = n
elementsl n (_:xs) = elementsl (n+1) xs

But I need to give two inputs: 0 and a list. how can I give only the list as a single input and still have a counter in my function?

Upvotes: 0

Views: 465

Answers (1)

AJF
AJF

Reputation: 11913

Very simple, define a new function, and define the 'helper' function in a where block:

elements ls = helper 0 ls --`helper' is your previous function, defined below:
    where helper n []     = n
          helper n (_:xs) = helper (1+n) xs

This will prevent helper from being used elsewhere, but allows you to write your function in this way.

However, you could avoid this tail-recursion entirely, and just write:

elements []     = 0
elements (_:xs) = 1 + elements xs

and therefore avoid the need for two arguments. This second style is generally considered more idiomatic haskell.

Upvotes: 3

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