[Haskell-beginners] Question on fromIntegral

[Jonathan Drews]

Hi Folks:

 I am using Glasgow Haskell Compilation System, version 9.2.4 on
OpenBSD 7.2. I am stumped by the following problem. If I run the
following program in ghci, then it works fine. Look:

fact :: Integer -> Integer
fact n = product [1..n]


term :: Double -> Double
term x  = x**4/fromIntegral(fact(4))

$ ghci
GHCi, version 9.2.4: https://www.haskell.org/ghc/  :? for help
ghci> :l seriesTermTest.hs 
[1 of 1] Compiling Main             ( seriesTermTest.hs, interpreted )
Ok, one module loaded.
ghci> term 1.0
4.1666666666666664e-2

However if I use fromIntegral inside a list comprehension like so:

fact :: Integer -> Integer
fact n = product [1..n]


expon :: Double -> Double
expon x  = sum [x**i/fromIntegral(fact(i)) | i <- [0..50]]

then I get the following error message:

$ ghci                         
GHCi, version 9.2.4: https://www.haskell.org/ghc/  :? for help
ghci> :l ePowerSeries.hs 
[1 of 1] Compiling Main             ( ePowerSeries.hs, interpreted )

ePowerSeries.hs:6:40: error:
    * Couldn't match expected type `Integer' with actual type `Double'
    * In the first argument of `fact', namely `(i)'
      In the first argument of `fromIntegral', namely `(fact (i))'
      In the second argument of `(/)', namely `fromIntegral (fact
(i))'
  |
6 | expon x  = sum [x**i/fromIntegral(fact(i)) | i <- [0..50]]
  |                                        ^
Failed, no modules loaded.

What am I doing wrong?

--
Kind regards,
Jonathan