Concat nesting list to string, Haskell

Question

I do string mingling:

main = do
    first <- getLine
    second <- getLine
    print (zip first second)

result: [('a','1'),('b','2'),('c','3')].

But how I can concate result to a1b2c3?

See this question: [Interleave List of Lists in Haskell](http://stackoverflow.com/questions/14186433/interleave-list-of-lists-in-haskell) — Rufflewind, Dec 10 '14 at 08:18

score 3 · Accepted Answer · answered Dec 10 '14 at 08:24

You have to do the following operations:

1) Convert the tuples inside the list to a single String which can be performed by a single map.

2) Concatenate the entire list

Prelude> let a = [('a','1'),('b','2'),('c','3')]
Prelude> let b = map (\(x,y) -> x : [y]) a
Prelude> b
["a1","b2","c3"]
Prelude> concat b
"a1b2c3"
Prelude> Prelude.foldl1' (++) b -- instead of concat you can do fold
"a1b2c3"

score 2 · Answer 2 · answered Dec 10 '14 at 13:19

2

You can also do this in one handy line

let a = [('a','1'),('b','2'),('c','3')]
uncurry ((. return) . (:)) =<< a

answered Dec 10 '14 at 13:19

Arnon

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score 1 · Answer 3 · answered Dec 10 '14 at 11:36

If I may add yet another (unnecessary) answer, just to show in how many (crazy) ways Haskell lets you think and solve a problem :)

Prelude Data.List> let input = [('a','1'),('b','2'),('c','3')]
Prelude Data.List> let (l1,l2) = unzip input
Prelude Data.List> let alt_stream s1 s2 = head s1:head s2:alt_stream (tail s1) (tail s2)
Prelude Data.List> take (length l1 * 2) $ alt_stream (cycle l1) (cycle l2)
"a1b2c3"

Concat nesting list to string, Haskell

3 Answers3