Haskell: readLn: Gives whatever type of data you want

In my previous post, I explained about read function, which takes a string and convert it to specific type.

Syntax

read "string" :: TypeToConvert

Prelude> read "10.02" :: Double
10.02
Prelude> read "10.02" :: Float
10.02
Prelude> read "10" :: Integer
10
Prelude> read "True" :: Bool
True

readLn is similar to read function, only difference is it gives back whatever type of value you want. You no need to specify destination type.

Prelude> :t readLn
readLn :: Read a => IO a

Sample.hs

factorial n = if n == 0 then 1 else n * factorial (n - 1)
 
main = 
    do  putStrLn "What is 5! ?"
        x <- readLn
        if x == factorial 5
            then putStrLn "You're right!"
            else putStrLn "You're wrong!"

$ ghc Sample.hs
[1 of 1] Compiling Main             ( Sample.hs, Sample.o )
Linking Sample ...
$ 
$ ./Sample
What is 5! ?
120
You're right!
$ 
$ ./Sample
What is 5! ?
123
You're wrong!

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