Calculatrice

calculatrice.hs

data Expr =
	  Num Float
	| Add Expr Expr
	| Sub Expr Expr
	| Mul Expr Expr
	| Div Expr Expr
	  deriving (Show)

a :: Expr
a = Div (Num 5) (Num 2.6)

eval :: Expr -> Float
eval (Num a)   = a
eval (Add a b) = eval a + eval b
eval (Sub a b) = eval a - eval b
eval (Mul a b) = eval a * eval b
eval (Div a b) = eval a / eval b

parse :: String -> [String]
parse [] = []
parse lst@(x:xs)
	| x == ' '            = parse xs
	| x `elem` "+-*/"     = [[x]] ++ parse xs
	| x `elem` ['0'..'9'] = [num] ++ parse (drop (length num) xs)
		where num = parseNum lst

parseNum :: String -> String
parseNum [] = []
parseNum (x:xs) =
	if x `elem` ['0'..'9']
		then [x] ++ parseNum xs
		else []

main =
	putStrLn $ show $ parse "223  +  6" -- [223, "+", 6]

{-
isAlpha, isNum, isAlphaNum, isIdent, isSymbol :: Char -> Bool
isAlpha c    = c `elem` ['a'..'z'] || c `elem` ['A'..'Z']
isNum c      = c `elem` ['0'..'9']
isAlphaNum c = isAlpha c || isNum c
isIdent c    = isAlpha c || isNum c || c `elem` ['_']
isSymbol c   = c `elem` "+-*/="

val :: Char -> String
val c
  | isAlpha c = "Alpha"
  | isNum c   = "Num"
  | otherwise = "Nothing"

parse :: String -> [String]
parse [] = []
parse (x:xs) = if isSymbol x
	then [[x]] ++ parse(xs)
	else [parseNum xs] ++ parse(rst)
	where (_, rst) = parseNum xs

parseNum :: String -> String -> (String, String)
parseNum [] accum = accum
parseNum (x:xs) accum = if isNum x
	then parseNum xs $ accum ++ [x]
	else (accum, xs)

parseSymbol :: String -> String -> String
parseSymbol (x:_) a = a 

main =
  -- putStrLn $ val $ parse "9+9"
  putStrLn $ show $ parseNum "231  +    42" -- ["231", "+", "42"]

parseString :: String -> String -> String
parseString [] accum = accum
parseString (x:xs) accum = if x == '"'
	then accum
	else parseString xs $ accum ++ [x]
-}