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I know you can convert a String to an number with read:

Prelude> read "3" :: Int 3 Prelude> read "3" :: Double 3.0

But how do you grab the String representation of an Int value?

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4 Answers 4

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344

The opposite of read is show.

Prelude> show 3 "3" Prelude> read $ show 3 :: Int 3
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7 Comments

@Lega: You may find this useful: haskell.org/hoogle/?hoogle=Int+-%3E+String.
@ KennyTM A LOT of people will find that link useful! A link alone is +1, but for showing how to use it... That's +10 Thanks :)
Note that some organizations/standards strongly discourage the use of "show" because of its extreme polymorphism. A type-specific function (or, worst case, wrapper around show) would be helpful.
@JonWatte "Might", not "would". At the level of generality of this question, I don't think your suggestion is actionable.
Is there a way to do this manually without usyng system functions?
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14

Anyone who is just starting with Haskell and trying to print an Int, use:

module Lib ( someFunc ) where someFunc :: IO () x = 123 someFunc = putStrLn (show x)
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2 Comments

More idiomatic for Haskell is putStrLn $ show x (using right-associative operator $)
@Arlind: As someone trying to learn Haskell I really appreciate an answer like this. I'm not trying to become a Haskell expert at this time. I'm just trying to get simple functions to work and show the results to the console. Later I can learn what is and isn't "idiomatic". Thanks for helping out a beginner :-)
7

An example based on Chuck's answer:

myIntToStr :: Int -> String myIntToStr x | x < 3 = show x ++ " is less than three" | otherwise = "normal"

Note that without the show the third line will not compile.

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2

You can use show:

show 3

What I want to add is that the type signature of show is the following:

show :: a -> String

And can turn lots of values into string not only type Int.

For example:

show [1,2,3]

Here is a reference:

https://hackage.haskell.org/package/base-4.14.1.0/docs/GHC-Show.html#v:show

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