An example program using haskell-qrencode library.

qrencode-test.hs

import qualified Data.QRCode as Q -- from `haskell-qrencode' package
import qualified Codec.Picture as P -- from `JuicyPixels' package
import qualified Codec.Picture.Png as P
import qualified Data.ByteString.Lazy as B

pixelPerCell = 5

main :: IO ()
main = do l <- getLine
          let version = Nothing -- auto
              errorLevel = Q.QR_ECLEVEL_M
              mode = Q.QR_MODE_EIGHT
          qr <- Q.encodeString l version errorLevel mode True
          let width = Q.getQRCodeWidth qr
              mat = Q.toMatrix qr
              pixelAt x y = let x' = x `div` pixelPerCell
                                y' = y `div` pixelPerCell
                                i = y'
                                j = x'
                            in if mat!!i!!j == 0 then maxBound else minBound :: P.Pixel8
              image = P.generateImage pixelAt (width*pixelPerCell) (width*pixelPerCell)
              encodedImage = P.encodePng image
          B.writeFile "out.png" encodedImage