CODEWITHSUNDEEP
listhaskelllist-comprehension
Vlad Balanescu
Vlad Balanescu

Reputation: 674

Next element in a list

I have a function in Haskell which returns me the successor of a card. I know how to access the card, using list comprehension, but not quite sure how to get the next card, so pos+1. Here is my code:

pCard :: Card->Deck->Card
pCard (K,C) _ = (A,S) --exception for last card
pCard crd pck = head [p | (pos,p) <- (zip [0..51] pck), crd==p]

Upvotes: 3

Views: 940

Answers (2)

the-konapie
the-konapie

Reputation: 601

You can make you your Card type instantiate the Enum typeclass by deriving Enum, then use the succ function to get the successor card. Note that passing the last card of the deck to succ will result in a runtime error, though it looks like your first pCard function body will account for that.

I just noticed that your Card type appears to be a tuple; I'm guessing you defined Card using the type keyword? In which case the solution I proposed above won't work without using GHC extensions.

Upvotes: 3

chi
chi

Reputation: 116139

Hint: use dropWhile (/= crd) pck to remove all the cards from the beginning until your card is found. Then, the first card remaining is crd. The one after that is the one you want.

Still, if pck is a deck in a standard order, looping over the whole deck to find the next card seems to be quite inefficient.

Upvotes: 3

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