CODEWITHSUNDEEP
haskell
cde33
cde33

Reputation: 27

defining the type of a function- int and float on haskell

I have a problem with defining the type of a function. In the cases of 1, 10, 11 and 12, I insert an Int and return a float, but in the case in which I insert an Int and return an Int the types doesn't match. I tried with pointsForSeventy:: Int->Float and also with pointsForSeventy:: Real a-> Int->a (I thought this one would work because Integrals and Fractionals are inside the Real numbers)

pointsForSeventy 1 = 5.5
pointsForSeventy 10 = 0.5
pointsForSeventy 11 = 0.5
pointsForSeventy 12 = 0.5
pointsForSeventy a = a

Thanks in advance

Upvotes: 0

Views: 1778

Answers (2)

chi
chi

Reputation: 116174

You need an explicit conversion:

pointsForSeventy 1 = 5.5
pointsForSeventy 10 = 0.5
pointsForSeventy 11 = 0.5
pointsForSeventy 12 = 0.5
pointsForSeventy a = fromIntegral a

Unlike several other programming languages, Haskell will never automatically perform automatic or implicit conversion between numeric types.

On the other hand, numeric literals belong to any numeric type. E.g. 1/2*0.5 :: Double will return 0.25 since all the three literals are Doubles. In some languages like C, instead, 1/2*0.5 evaluates to 0 since 1/2 is integer division (!), and evaluates to 0.

Upvotes: 3

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 477170

Haskell is a statically typed language. So that means that the return type can not depend on the value of the input.

An idea might be to convert the Int into a Float by using fromIntegral :: (Integral a, Num b) => a -> b:

pointsForSeventy :: Int -> Float
pointsForSeventy 1 = 5.5
pointsForSeventy 10 = 0.5
pointsForSeventy 11 = 0.5
pointsForSeventy 12 = 0.5
pointsForSeventy a = fromIntegral a

In case you want to treat the Int case different from the Float case, you can also use Either:

pointsForSeventy :: Int -> Either Float Int
pointsForSeventy 1 = Left 5.5
pointsForSeventy 10 = Left 0.5
pointsForSeventy 11 = Left 0.5
pointsForSeventy 12 = Left 0.5
pointsForSeventy a = Right a

Upvotes: 4

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