程序代写CS代考 Haskell – Calculator example from chapter 13 of Programming in Haskell, – cscodehelp代写
— Calculator example from chapter 13 of Programming in Haskell,
— , Cambridge University Press, 2016.
import Parsing
import System.IO
— Expression parser
expr :: Parser Int
expr = do t <- term
do symbol "+"
e <- expr
return (t + e)
<|> do symbol “-”
e <- expr
return (t - e)
<|> return t
term :: Parser Int
term = do f <- factor
do symbol "*"
t <- term
return (f * t)
<|> do symbol “/”
t <- term
return (f `div` t)
<|> return f
factor :: Parser Int
factor = do symbol “(”
e <- expr
symbol ")"
return e
<|> integer
— IO utilities
getCh :: IO Char
getCh = do hSetEcho stdin False
x <- getChar
hSetEcho stdin True
return x
beep :: IO ()
beep = putStr "BEL"
cls :: IO ()
cls = putStr "ESC[2J"
writeat :: (Int,Int) -> String -> IO ()
writeat p xs = do goto p
putStr xs
goto :: (Int,Int) -> IO ()
goto (x,y) = putStr (“ESC[” ++ show y ++ “;” ++ show x ++ “H”)
— Calculator
box :: [String]
box = [“+—————+”,
“| |”,
“+—+—+—+—+”,
“| q | c | d | = |”,
“+—+—+—+—+”,
“| 1 | 2 | 3 | + |”,
“+—+—+—+—+”,
“| 4 | 5 | 6 | – |”,
“+—+—+—+—+”,
“| 7 | 8 | 9 | * |”,
“+—+—+—+—+”,
“| 0 | ( | ) | / |”,
“+—+—+—+—+”]
buttons :: String
buttons = standard ++ extra
where
standard = “qcd=123+456-789*0()/”
extra = “QCD ESCBSDEL
”
showbox :: IO ()
showbox = sequence_ [writeat (1,y) b | (y,b) <- zip [1..] box]
display xs = do writeat (3,2) (replicate 13 )
writeat (3,2) (reverse (take 13 (reverse xs)))
calc :: String -> IO ()
calc xs = do display xs
c <- getCh
if elem c buttons then
process c xs
else
do beep
calc xs
process :: Char -> String -> IO ()
process c xs | elem c “qQESC” = quit
| elem c “dDBSDEL” = delete xs
| elem c “=
” = eval xs
| elem c “cC” = clear
| otherwise = press c xs
quit :: IO ()
quit = goto (1,14)
delete :: String -> IO ()
delete [] = calc []
delete xs = calc (init xs)
eval :: String -> IO ()
eval xs = case parse expr xs of
[(n,[])] -> calc (show n)
_ -> do beep
calc xs
clear :: IO ()
clear = calc []
press :: Char -> String -> IO ()
press c xs = calc (xs ++ [c])
run :: IO ()
run = do cls
showbox
clear
