CODEWITHSUNDEEP
listhaskellfilter
nurgasemetey
nurgasemetey

Reputation: 770

filter function containing another function in predicate

I have a question about filter. How can I make that my function (manhattanDistance) will take each element in list and use it for itself? Can you explain how it can be implemented?

func :: [(Int,Int)] ->
        (Int, Int, [Char], [Char], [Char], [Char],
                   [Char], [Char], [Char], [Char]) ->
        [(Int,Int)]
func (x:xs) agent  = filter ((manhattanDistance x agentCoord(agent)) == 1) (x:xs)

Upvotes: 1

Views: 100

Answers (1)

Nikita Volkov
Nikita Volkov

Reputation: 43309

The problem was that you weren't using the filter's lambda parameter, and referring to a head of the outer function's list instead. Here's a corrected version:

func 
  :: [(Int, Int)] 
  -> (Int, Int, [Char], [Char], [Char], [Char], [Char], [Char], [Char], [Char]) 
  -> [(Int, Int)]
func xs agent = 
  filter (\e -> manhattanDistance e (agentCoord agent) == 1) xs

By the way, that tuple you have should be normalized to ADTs. It's commonly considered a bad practice to use such huge tuples and by the readability of your function's signature you can kinda see why.

Upvotes: 4

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