Что-то похожее на правду

coursework/part1/src/Lib.hs

@@ -48,3 +48,39 @@ char c = satisfy (== c)
 
 digit :: Parser Char Char
 digit = satisfy isDigit
+
+skipSpaces :: Parser Char String
+skipSpaces = many (char ' ')
+
+number :: Parser Char Int
+number = skipSpaces *> (strToInt <$> some digit)
+    where 
+        strToInt = foldl (\acc x -> acc * 10 + digitToInt x) 0
+
+data Operation = Add | Sub | Mul | Div deriving Show
+
+operationToString :: Operation -> String
+operationToString op = case op of
+    Add -> " + "
+    Sub -> " - "
+    Mul -> " * "
+    Div -> " / " 
+
+operationToOperator :: Operation -> (Int -> Int -> Int)
+operationToOperator op = case op of
+    Add -> (+)
+    Sub -> (-)
+    Mul -> (*)
+    Div -> div 
+    
+
+operation :: Parser Char Operation
+operation = skipSpaces *> (
+        char '+' *> pure Add <|>
+        char '-' *> pure Sub <|>
+        char '*' *> pure Mul <|>
+        char '/' *> pure Div
+    )
+
+expression :: Parser Char (Int, Operation, Int)
+expression = (,,) <$> number <*> operation <*> number <* skipSpaces