CODEWITHSUNDEEP
haskell
user2999428
user2999428

Reputation: 165

Length l1 +1 => what is one for?

agrupa :: String -> [(Char,Int)]

agrupa [ ] = [ ] 

agrupa (x:xs) = let (l1, l2) = span' (==x) xs  

                in (x, (length l1) + 1) : agrupa l2 

span' :: (a->Bool) -> [a] -> ([a],[a])

span' p l = (takeWhile p l, dropWhile p l)

this function gets a string and gives us how many of each character are there?

my question is related to the 1 in (length l1) + 1 why do we need it? I'd really appreciate if you explain it with different example because such cases (like+1) I've seen lots of times also in scan( or debug only the agrope part please) the function to see how it works exactly?

thanks for your time

Upvotes: 0

Views: 108

Answers (1)

leftaroundabout
leftaroundabout

Reputation: 120711

The + 1 is there because you've previously matched one of the == x elements away, namely x itself, in the pattern (x:xs). If you didn't consider that, a list with no duplicates would give all 0s in the snd of each tuple in the result; as you have it the snd always gives the actual number of consecutive elements.

Upvotes: 6

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