Question

import Data.Char

main = do 
    c <- getChar
    if not $ isUpper c
        then do putChar $ toUpper c
                main
        else putChar '\n'

Loading and executing in GHCi:

λ> :l foo.hs
Ok, modules loaded: Main.
λ> main
ñÑsSjJ44aAtTR
λ>

This consumes one character at time.

But in a terminal:

[~ %]> runhaskell foo.hs
utar,hkñm-Rjaer 
UTAR,HKÑM-
[~ %]>

it consumes one line at time.

Why does it behave differently?

Answer 1

When you run a program in terminal it uses LineBuffering by default, but in ghci it is set to NoBuffering. You can read about it here. You will have to remove buffering from stdin and stdout to get the similar behavior.

import Data.Char
import System.IO

main = do
    hSetBuffering stdin NoBuffering
    hSetBuffering stdout NoBuffering
    foo
foo = do
    c <- getChar
    if not $ isUpper c
        then do putChar $ toUpper c
                foo
        else putChar '\n'