How to apply higher order function to an effectful function in Haskell?

Question

I have too functions:

higherOrderPure :: (a -> b) -> c
effectful :: Monad m => (a -> m b)

I\'d like to apply the first function

Answer 1

I think you can achieve what you want by writing a monadic version of curve:

curveM :: Monad m => (Double -> m Double) -> m (QDiagram B R2 Any)
curveM f = do
    let xs = [1..100]
    ys <- mapM f xs
    let pts = map p2 $ zip xs ys
    return $ fromVertices pts

This can easily be written shorter, but it has the type you want. This is analogous to map -> mapM and zipWith -> zipWithM. The monadic versions of the functions have to be separated out into different implementations.

---

To test:

func1, func2 :: Double -> Either String Double
func1 x = if x < 1000 then Right x else Left "Too large"
func2 x = if x < 10   then Right x else Left "Too large"

> curveM func1
Right (_ :: QDiagram B R2 Any)
> curveM func2
Left "Too large"