CODEWITHSUNDEEP
haskellrecursionconcatenation
kiroyuu
kiroyuu

Reputation: 59

Haskell own concat method with recursion

Im practicing recursion on Haskell and need to do concat method with own impelentation on a nested list.

I've tried 

    myConcat :: [[a]] -> [a]
    myConcat [[]] = []
    myConcat ((x:xs)) = x : myConcat ((xs))

But it doesnt seem to work.

myConcat [[1,2],[3,4,5],[6]] == [1,2,3,4,5,6]

This is the goal.

The main problem is that i dont really know how to work with nested lists.

Upvotes: 0

Views: 2159

Answers (2)

nader.h
nader.h

Reputation: 505

hello you have just to replace your x : myConcat xs by x ++ myConcat xs

Upvotes: 1

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476719

Since x is a list here (it has type [a]), you can not use x : … here, unless you again want to create a list of lists, but then your myConcat would act like an id function for lists.

You here need to append x with the rest of the list, so you can use (++) :: [a] -> [a] -> [a], indeed:

myConcat :: [[a]] -> [a]
myConcat [] = []
myConcat (x:xs) = x ++ myConcat xs

Note that you forgot the base case []. By writing [[]] you match a list with one element: the empty list. That is something different.

Upvotes: 5

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