CODEWITHSUNDEEP
haskell
jamie
jamie

Reputation: 176

Haskell keeps giving me type errors

Don't know what I'm doing wrong

type Name = String
type Location = (Float,Float)
type RainfallFigures = [Int]
type Place = (Name,Location,RainfallFigures)

rtnClosestDryPlace :: (Location -> Int -> [Place] -> [(Name,Float)]) -> (Name,Float)
rtnClosestDryPlace p1 n ((a,p2,c):xs) = rtnLowestDistance (distanceList p1 (rtnFullDryPlaces ((a,p2,c):xs) n))

    Couldn't match expected type ‘(Name, Float)’
                      with actual type ‘Int
                    -> [(Name, Location, RainfallFigures)] -> (Name, Float)’
        • The equation(s) for ‘rtnClosestDryPlace’ have three arguments,
          but its type ‘(Location -> Int -> [Place] -> [(Name, Float)])
                        -> (Name, Float)’
          has only one
    rtnClosestDryPlace p1 n ((a,p2,c):xs) = rtnLowestDistance (distanceList p1 (rtnFullDryPlaces ((a,p2,c):xs) n))
       | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^



    template.hs:90:73: error:
        • Couldn't match expected type ‘(Float, Float)’
                      with actual type ‘Location -> Int -> [Place] -> [(Name, Float)]’
        • Probable cause: ‘p1’ is applied to too few arguments
          In the first argument of ‘distanceList’, namely ‘p1’
          In the first argument of ‘rtnLowestDistance’, namely
            ‘(distanceList p1 (rtnFullDryPlaces ((a, p2, c) : xs) n))’
          In the expression:
            rtnLowestDistance
              (distanceList p1 (rtnFullDryPlaces ((a, p2, c) : xs) n))
       |
    90 | rtnClosestDryPlace p1 n ((a,p2,c):xs) = rtnLowestDistance (distanceList p1 (rtnFullDryPlaces ((a,p2,c):xs) n))
       |          ^^

Location, Int, [place] all get sent to a function which returns [(Name, Float)], which in turn gets sent to a function which returns (Name,Float) I don't know why this program can't run. Why can it not match the types

Edit: After rewriting the function I’ve managed to correctly write it down with no matching errors

Upvotes: 1

Views: 70

Answers (1)

chi
chi

Reputation: 116139

Your type is wrong:

rtnClosestDryPlace :: (Location -> Int -> [Place] -> [(Name,Float)]) -> (Name,Float)

means that rtnClosestDryPlace is a function whose input argument has type

(Location -> Int -> [Place] -> [(Name,Float)])

and whose output argument has type

(Name,Float)

So, that type promises that, given a 3-arguments function, the code below is able to return a pair. That's not what you want.

I guess you actually want something like

rtnClosestDryPlace :: Location -> Int -> [Place] -> [(Name,Float)]

Upvotes: 4

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