Import another file in Haskell

In Haskell, we can import another source file into our current code with the import keyword. This allows us to use functions or types defined in that file in our current project.

Let's say we have two files named "File1.hs" and "File2.hs" in the same directory. If we want to import functions/types defined in "File1.hs" into "File2.hs", we can use the following syntax:

-- File2.hs
module File2 where
import File1 -- import File1.hs
-- rest of the code here

In this example, we first declare the module name (File2) using the module keyword. Then, we use the import keyword to import the functions/types defined in "File1.hs". We don't need to include the .hs extension in the import statement.

In "File1.hs", we could define some functions like:

-- File1.hs
module File1 where
myFunction :: Int -> Int

myFunction x = x + 1

Now, in "File2.hs", we can use the myFunction function from "File1.hs":

-- File2.hs
module File2 where
import File1
main = do

  putStrLn "Enter a number:"

  num <- readLn :: IO Int

  let result = myFunction num

  putStrLn ("The result is: " ++ show result)

In this example, we import File1 and use the myFunction function that was defined in that file. We can then use myFunction in our main program to transform user input.

Note that when we import a module, we can import all its definitions or selectively import just a few of them, like this:

import File1 (myFunction, anotherFunction)

This would only import myFunction and anotherFunction from "File1.hs".