Question

One way to calculate 2^8 in haskell is by writing

product(replicate 8 2)

When trying to create a function for this, defined as follows…

power1 :: Integer →  Integer → Integer
power1 n k | k < 0 = error errorText
power1 n 0 = 1
power1 n k = product(replicate k n)

i get the following error:

Couldn't match expected type 'Int' against inferred type 'Integer'

My guess is that I must use the fromInteger function somewhere… I’m just not sure where or how? Is it an interface or what is fromInteger, and how should I use it?

Thanks

Answer 1

Firstly, never use fromInteger. Use fromIntegral.

You can see where the type error is by looking at the type of replicate:

replicate :: Int -> a -> [a]

so when you giv it ‘k’ as an argument, which you’ve asserted is an Integer via the type declaration, we have a type error.

A better approach for this would be to use genericReplicate:

genericReplicate :: (Integral i) => i -> a -> [a]

So then:

power1 n k = product (genericReplicate k n)