To install GHC (Glasgow Haskell Compiler; containing also GHCI, its interpreted version)
on Windows, go to
https://www.haskell.org/ghcup/
and follow the instruction.

Write your code in a file with the extension ".hs"
 
Let’s start now with an example GHCi session. 

First open Windows PowerShell.

You can fire up GHCi with the command ghci:

$ ghci
GHCi, version 8.y.z: https://www.haskell.org/ghc/  :? for help
ghci>

There may be a short pause while GHCi loads the prelude and standard libraries, after which the prompt is shown.

Haskell expressions can be typed at the prompt:

ghci> 1+2
3
ghci> let x = 42 in x / 9
4.666666666666667
ghci>

Loading source files

Suppose we have writte the following Haskell source codein a file example.hs:


fac 0 = 1
fac n = n * fac (n-1)

You can save example.hs anywhere you like, but if you save it somewhere other than the current directory then we will need to change to the right directory in GHCi:

ghci> :cd <the path to the directory containing example.hs>

To load a Haskell source file into GHCi, use the :load command:

ghci> :load example
Compiling example             ( example.hs, interpreted )
Ok, modules loaded: example.
*ghci>

GHCi has loaded the example module, and the prompt has changed to *ghci> to indicate that the current context for expressions typed at the prompt is the example module we just loaded. So we can now type expressions involving the functions from Main.hs:

*ghci> fac 17
355687428096000