When I load the following code in ghci I get a Monomomorphism restriction warning with the suggested fix of
Consider giving ‘pexp’ and ‘nDividedByPExp’ a type signature
|
17 | (nDividedByPExp, pexp) = getPExp' nDividedByP 1
but doing that doesn't solve the problem. I then get the error:
Overloaded signature conflicts with monomorphism restriction
nDividedByPExp :: Integral i => i
Here is the code:
{-# OPTIONS_GHC -Wall -fno-warn-incomplete-patterns #-}
{-# LANGUAGE ExplicitForAll, ScopedTypeVariables #-}
pfactor :: forall i. Integral i => i -> [(i, i)]
-- pfactor :: Integral i => i -> [(i, i)]
pfactor m =
pf' m [] $ primesUpTo (floorSqrt m)
where
pf' :: Integral i => i -> [(i, i)] ->[i] -> [(i, i)]
pf' n res (p : ps)
| pIsNotAFactor = pf' n res ps
| otherwise = pf' nDividedByPExp ((p, pexp) : res) remainingPrimes
where
(nDividedByP, r) = n `quotRem` p
pIsNotAFactor = r /= 0
-- nDividedByPExp, pexp :: Integral i => i
(nDividedByPExp, pexp) = getPExp' nDividedByP 1
-- getPExp' :: Integral i => i -> i -> (i, i)
getPExp' currNDividedByP currExp
| pDoesNotDivideCurrNDividedByP = (currNDividedByP, currExp)
| otherwise = getPExp' q1 (currExp + 1)
where
-- q1, r1 :: Integral i => i
(q1, r1) = currNDividedByP `quotRem` p
pDoesNotDivideCurrNDividedByP = r1 /= 0
remainingPrimes = takeWhile (<= floorSqrt nDividedByPExp) ps
floorSqrt :: Integral i => i -> i
floorSqrt = undefined
primesUpTo :: Integral i => i -> [i]
primesUpTo = undefined
I tried adding the declaration in commented line 16 as suggested but that resulted in an error as I described above.
I've deleted some lines from the actual code to make it simpler. I don't expect the code above to run properly but I do expect it to compile without warnings. I don't understand how to fix the warning I am getting.
When you declare their types as nDividedByPExp, pexp :: Integral i => i
, it'll be treated as nDividedByPExp, pexp :: forall i. Integral i => i
. This i
and the i
declared at the top level will be different types even though you brought the latter to the scope using ScopedTypeVariables
. Also, i
is still polymorphic.
You can declare it as nDividedByPExp, pexp :: i
, where i
refers to the i
at the top level which is bound to a specific type so is monomorphic.