add 'Parser' with basic parsing infrastructure

also: - TokenType: derive 'Eq' instance
ccntrq · Jan 6, 2018 · 6f44a50 · 6f44a50
1 parent 1eeb10e
commit 6f44a50
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Showing 2 changed files with 51 additions and 1 deletion.
diff --git a/src/Parser.hs b/src/Parser.hs
@@ -0,0 +1,50 @@
+module Parser where
+
+import Expr
+import Stmt
+import Token
+import TokenType
+
+import Control.Conditional
+
+import Control.Monad.State
+import Control.Monad.Except
+import Control.Monad.Identity
+
+data ParserState = ParserState
+    { tokens :: [Token]
+    , current :: Int   
+    } deriving (Show)
+
+data ParserError = ScannerError Token String deriving (Show)
+
+type Parser a = ExceptT ParserError (StateT ParserState Identity) a
+
+runParser :: ParserState -> Parser a -> Either ParserError a
+runParser st p = runIdentity $ evalStateT (runExceptT p) st
+
+initState :: [Token] -> ParserState
+initState ts = ParserState ts 0
+
+parse :: Parser [Stmt]
+parse = parse' [] 
+  where
+    parse' acc = ifM isAtEnd (return $ reverse acc) (declaration >>= \d -> parse' d:acc)
+
+check :: TokenType -> Parser Bool
+check tokenType = ifM isAtEnd (return False) (peek >>= \t -> return $ t_type t == tokenType)
+
+advance :: Parser Token
+advance = ifM isAtEnd (previous) (incCurrent >> previous)
+
+isAtEnd :: Parser Bool
+isAtEnd = peek >>= \t -> if' (t_type t == EOF) (return True) (return False)
+
+peek :: Parser Token
+peek = get >>= \s -> return $ tokens s !! current s
+
+previous :: Parser Token
+previous = get >>= \s -> return $ tokens s !! (current s - 1)
+
+incCurrent :: Parser ()
+incCurrent = get >>= \s -> put s {current = current s +1}
diff --git a/src/TokenType.hs b/src/TokenType.hs
@@ -46,4 +46,4 @@ data TokenType
   | EOF
   -- Throwaway token for comment/whitespace
   | WS
-  deriving (Show)
+  deriving (Show, Eq)