1 files changed, 48 insertions, 0 deletions
diff --git a/parser.hs b/parser.hs
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--- /dev/null
+++ b/parser.hs
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+module Parser where
+
+import Control.Applicative
+
+
+newtype Parser a = Parser { runParser :: String -> Maybe (a, String) }
+
+instance Functor Parser where
+    fmap f (Parser p) = Parser new_p
+        where new_p s = do
+                (x, s') <- p s
+                return (f x, s')
+
+instance Applicative Parser where
+    pure x = Parser (\s -> Just (x, s))
+    (Parser p1) <*> (Parser p2) = Parser new_p
+        where new_p s = do
+                (f, s') <- p1 s
+                (x, s'') <- p2 s'
+                return (f x, s'')
+    -- (Parser p1) *> (Parser p2) = Parser new_p
+    -- (Parser p1) <* (Parser p2) = Parser new_p
+
+instance Alternative Parser where
+    empty = Parser (\_ -> Nothing)
+    (Parser p1) <|> (Parser p2) = Parser new_p
+        where new_p s = p1 s <|> p2 s
+
+
+data Equation
+    = EquationAdd
+    | EquationSub
+    | EquationMul
+    -- | EquationDiv ?
+    | EquationExp
+    | EquationEqu
+    | EquationNum Float
+
+charP :: Char -> Parser Char
+charP c = Parser f
+    where f ""     = Nothing
+          f (c:cs) = Just (c, cs)
+
+-- equationAddP :: Parser Equation
+-- equationAddP = charP '+' *> EquationAdd
+
+-- equationP :: Parser Equation
+-- equationP =