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  1. main = do
  2.  void initGUI -- allocates some resources and prepares GTK+ for work, also parses command line arguments
  3.  window <- windowNew -- :: Window
  4.  set window [ windowTitle := "Calculator", windowResizable := False, windowDefaultWidth := 230, windowDefaultHeight := 250 ]
  5.  
  6.  display <- entryNew -- Entry - a single line text entry widget
  7.  set display [ entryEditable := False, entryXalign := 1 , entryText := "0" ]
  8.  
  9.  grid <- gridNew
  10.  gridSetRowHomogeneous grid True
  11.  let attach x y w h item = gridAttach grid item x y w h
  12.  attach 0 0 5 1 display
  13.   mkBtn "MC" display >>= attach 0 1 1 1
  14.   mkBtn "MR" display >>= attach 1 1 1 1
  15.   mkBtn "MS" display >>= attach 2 1 1 1
  16.   mkBtn "M+" display >>= attach 3 1 1 1
  17.   mkBtn "M-" display >>= attach 4 1 1 1
  18.   mkBtn "âĘŘ" display >>= attach 0 2 1 1
  19.   mkBtn "CE" display >>= attach 1 2 1 1
  20.   mkBtn "C" display >>= attach 2 2 1 1
  21.   mkBtn "Âś" display >>= attach 3 2 1 1
  22.   mkBtn "âĹŽ" display >>= attach 4 2 1 1
  23.   mkBtn "7" display >>= attach 0 3 1 1
  24.   mkBtn "8" display >>= attach 1 3 1 1
  25.   mkBtn "9" display >>= attach 2 3 1 1
  26.   mkBtn "Ãů" display >>= attach 3 3 1 1
  27.   mkBtn "%" display >>= attach 4 3 1 1
  28.   mkBtn "4" display >>= attach 0 4 1 1
  29.   mkBtn "5" display >>= attach 1 4 1 1
  30.   mkBtn "6" display >>= attach 2 4 1 1
  31.   mkBtn "*" display >>= attach 3 4 1 1
  32.   mkBtn "1/x" display >>= attach 4 4 1 1
  33.   mkBtn "1" display >>= attach 0 5 1 1
  34.   mkBtn "2" display >>= attach 1 5 1 1
  35.   mkBtn "3" display >>= attach 2 5 1 1
  36.   mkBtn "âĂŞ" display >>= attach 3 5 1 1
  37.   mkBtn "=" display >>= attach 4 5 1 2
  38.   mkBtn "0" display >>= attach 0 6 2 1
  39.   mkBtn "." display >>= attach 2 6 1 1
  40.   mkBtn "+" display >>= attach 3 6 1 1
  41.   containerAdd window grid
  42.  
  43.  widgetShowAll window
  44.  mainGUI -- main loop
  45.  
  46.  btnOnActivated :: Entry -> String -> IO ()
  47.   btnOnActivated display label = do
  48.   text <- get display entryText
  49.   case label of
  50.   "âĹŽ" -> set display [ entryText := show (sqrt (read text)) ]
  51.   otherwise -> set display [ entryText := text++label ]
  52.  
  53.  mkBtn :: String -> Entry -> IO Button
  54.   mkBtn label display= do
  55.   btn <- buttonNew
  56.   set btn [ buttonLabel := label ]
  57.   on btn buttonActivated (btnOnActivated display label)
  58.   return btn
  59.  
Compilation error #stdin compilation error #stdout 0s 0KB
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stdin
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Standard input is empty
compilation info 
[1 of 1] Compiling Main             ( prog.hs, prog.o )

prog.hs:47:32: error:
    parse error on input ‘=’
    Perhaps you need a 'let' in a 'do' block?
    e.g. 'let x = 5' instead of 'x = 5'
stdout
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Standard output is empty
https://ideone.com/8zoVW2
language:
Haskell (ghc 8.4.4)
created:
6 years ago
visibility:
public

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