CODEWITHSUNDEEP
haskell
hahcho
hahcho

Reputation: 1409

IO monad arguments usage without IO

I am having this issue the function calculate accepts IO a type and I already have a function that return the same thing but it accepts a as her type. Below is my code. I have been searching around the web for some time but i couldn't manage to fix my error.Tahnks in advance for your help.

pureCalculate :: Expr (Double -> Double -> Double) -> Map.Map String Double -> Double

calculate :: IO(Expr (Double -> Double -> Double)) -> Map.Map String Double -> IO Double

calculate expr args =
    do let x = pureCalculate expr args
       return x

Upvotes: 1

Views: 157

Answers (1)

bheklilr
bheklilr

Reputation: 54058

I believe you want to do something like

calculate ioexpr args = do
    expr <- ioexpr
    return $ pureCalculate expr args

In order to use a value wrapped in the IO monad, you first have to extract it using <- notation, or you can use other functions like fmap to map a function to the contents.

If you wanted to use fmap in this case, you could do something like

calculate ioexpr args = fmap (\expr -> pureCalculate expr args) ioexpr

Which is equivalent to

calculate ioexpr args = fmap (`pureCalculate` args) ioexpr

or

calculate ioexpr args = fmap (flip pureCalculate args) ioexpr

Upvotes: 6

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