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Finding type signatures in Haskell that are too specific


Finding type signatures in Haskell that are too specific

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Finding type signatures in Haskell that are too specific
Tag : haskell , By : Porta
Date : November 25 2020, 01:01 AM


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Simplify Haskell Type Signatures


Tag : haskell , By : potix2
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further ghci tells us
add :: Num a => (a -> a -> a) -> a -> a -> a

When are type signatures necessary in Haskell?


Tag : haskell , By : Juan Pablo
Date : March 29 2020, 07:55 AM
it should still fix some issue Monomorphism restriction
If you have MonomorphismRestriction enabled, then sometimes you will need to add a type signature to get the most general type:
{-# LANGUAGE MonomorphismRestriction #-}
-- myPrint :: Show a => a -> IO ()
myPrint = print
main = do
  myPrint ()
  myPrint "hello"
myValue :: Read a => a
myValue = read "0"

myTuple :: Read a => (a, String)
myTuple = (myValue, "hello")
myString = snd myTuple
myString = snd (myTuple :: ((), String))

Haskell type signatures: Question on type signature of lastButOne Program


Tag : haskell , By : Mforg
Date : March 29 2020, 07:55 AM
To fix the issue you can do I'm reading through Real World Haskell and one of the exercises is to construct a function lastButOne, which simply returns the second to last element of a list. , You can acomplish that with pattern matching like:
lastButOne :: [a] -> a
lastButOne []    = error "not elements"
lastButOne [x]   = x
lastButOne [x,_] = x
lastButOne (x:xs) = lastButOne xs

Type Signatures in Haskell


Tag : haskell , By : Stone
Date : March 29 2020, 07:55 AM

Haskell Type Signatures


Tag : haskell , By : AdrianB
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , Those are constraints to a polymorphic type.
Haskell, despite being statically typed, makes it very easy to write function that can work with different types, through a system called parametric polymorphism. I'll first give all your functions concrete (monomorphic) signatures instead:
mult :: [Integer] -> Integer
mult  = foldl' (*) 1  -- foldl' is better for performance/memory than foldr

posList :: [Integer] -> [Integer]
posList = filter (>0) 

trueList :: [Bool] -> Bool
trueList  =  foldl' (&&) True

evenList :: [Integer] -> Bool
evenList x = foldl' (+) 2 x `mod` 2 == 0
            -- `if True then True else False` is tautological
mult :: ∀ a . [a] -> a
mult :: [a] -> a
mult :: Num a => [a] -> a
posList :: [a] -> [a]
posList :: (Num a, Ord a) => [a] -> [a]
evenList :: Integral a => [a] -> Bool
evenList :: (Integral a, Foldable t) => t a -> Bool
mult :: (Num a, Foldable t) => t a -> a
trueList :: Foldable t => t Bool -> Bool
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