How to convert IO Int to String in Haskell?

Question

I'm learning to use input and output in Haskell. I'm trying to generate a random number and output it to another file. The problem is that the random number seems to be returning an IO Int, something that I can't convert to a String using show.

Could someone give me a pointer here?

Answer 1

It's helpful if you show us the code you've written that isn't working.

Anyway, you are in a do block and have written something like this, yes?

main = do
    ...
    writeFile "some-file.txt" (show generateRandomNumberSomehow)
    ...

You should instead do something like this:

main = do
    ...
    randomNumber <- generateRandomNumberSomehow
    writeFile "some-file.txt" (show randomNumber)
    ...

The <- operator binds the result of the IO Int value on the right to the Int-valued variable on the left. (Yes, you can also use this to bind the result of an IO String value to a String-valued variable, etc.)

This syntax is only valid inside a do block. It's important to note that the do block will itself result in an IO value --- you can't launder away the IO-ness.