An example program using haskell-qrcode library.

qrcode-test.hs

import qualified Codec.Binary.QRCode as Q -- from `qrcode' package
import qualified Codec.Picture as P -- from `JuicyPixel' package
import qualified Codec.Picture.Png as P
import qualified Data.ByteString.Lazy as B
import Data.Array (Array,bounds,(!))

pixelPerCell = 5

main :: IO ()
main = do l <- getLine
          let Just version = Q.version 1
              errorLevel = Q.L -- or Q.M, Q.Q, Q.H
              mode = Q.Alphanumeric -- or Q.Numeric
              array :: Array (Int,Int) P.Pixel8
              Just array = fmap Q.toArray (Q.encode version errorLevel mode l)
              ((y0,x0),(y1,x1)) = bounds array
              pixelAt x y = let x' = x `div` pixelPerCell
                                y' = y `div` pixelPerCell
                                i = y'+y0
                                j = x'+x0
                            in array!(i,j)
              image = P.generateImage pixelAt ((x1-x0+1)*pixelPerCell) ((y1-y0+1)*pixelPerCell)
              encodedImage = P.encodePng image
          B.writeFile "out.png" encodedImage