scanner first steps

src/Lox/Scanner.hs

@@ -0,0 +1,92 @@
+module Lox.Scanner where
+
+import Control.Monad.State.Lazy
+import Control.Monad.Extra
+
+data TokenType = LEFT_PAREN | RIGHT_PAREN | LEFT_BRACE | RIGHT_BRACE 
+               | COMMA | DOT | MINUS | PLUS | SEMICOLON | SLASH | STAR
+               | BANG | BANG_EQUAL
+               | EQUAL | EQUAL_EQUAL
+               | GREATER | GREATER_EQUAL
+               | LESS | LESS_EQUAL
+               | IDENTIFIER | STRING | NUMBER
+               | AND | CLASS | ELSE | FALSE | FUN | FOR | IF | NIL | OR
+               | PRINT | RETURN | SUPER | THIS | TRUE | VAR | WHILE
+               | EOF
+    deriving Show
+
+-- undefined for now
+data Object = NullObject deriving Show
+
+data Token = Token {
+    getType :: TokenType, 
+    getLexeme :: String,
+    getObject :: Object,
+    getLineNumber :: Int
+} deriving Show
+
+data ScannerState = ScannerState {source :: String, tokens :: [Token]}
+
+emptyScannerState :: String -> ScannerState
+emptyScannerState source = ScannerState {source=source, tokens=[]}
+
+scanTokensFromSource :: String -> [Token]
+scanTokensFromSource source = evalState scanTokens (emptyScannerState source)
+
+scanTokens :: State ScannerState [Token]
+scanTokens = whileM (scanToken >> (not <$> isAtEnd)) >> gets (reverse . tokens)
+
+isAtEnd :: State ScannerState Bool
+isAtEnd = gets scannerIsAtEnd
+
+scannerIsAtEnd :: ScannerState -> Bool
+scannerIsAtEnd ScannerState {source=source, tokens=_} = null source
+
+scanToken :: State ScannerState ()
+scanToken = do
+    c <- advance
+    token <- case c of
+        '(' -> addToken LEFT_PAREN
+        ')' -> addToken RIGHT_PAREN
+        '{' -> addToken LEFT_BRACE
+        '}' -> addToken RIGHT_BRACE
+        ',' -> addToken COMMA
+        '.' -> addToken DOT
+        '-' -> addToken MINUS
+        '+' -> addToken PLUS
+        ';' -> addToken SEMICOLON
+        '*' -> addToken STAR
+        '!' -> ifM (match '=') (addToken BANG_EQUAL) (addToken BANG)
+        '=' -> ifM (match '=') (addToken EQUAL_EQUAL) (addToken EQUAL)
+        '<' -> ifM (match '=') (addToken LESS_EQUAL) (addToken LESS)
+        '>' -> ifM (match '=') (addToken GREATER_EQUAL) (addToken GREATER)
+        _ -> error "Lexical error" -- TODO error handling
+    return ()
+
+advance :: State ScannerState Char
+advance = state scannerAdvance
+
+scannerAdvance :: ScannerState -> (Char, ScannerState)
+scannerAdvance ScannerState {source=(c:cs), tokens=tokens} = (c, ScannerState {source=cs, tokens=tokens})
+
+match :: Char -> State ScannerState Bool
+match c = state (scannerMatch c)
+
+scannerMatch :: Char -> ScannerState -> (Bool, ScannerState)
+scannerMatch matchChar ScannerState {source=(sourceChar:sourceTail), tokens=tokens} = (matchChar == sourceChar, ScannerState {source=source, tokens=tokens})
+    where source = if matchChar == sourceChar then sourceTail else sourceChar : sourceTail
+scannerMatch _ state@ScannerState {source="", tokens=_} = (False, state)
+
+peek :: State ScannerState Char
+peek = gets $ head . source
+
+addToken :: TokenType -> State ScannerState ()
+addToken token = modify $ scannerAddLiteralToken token NullObject
+
+addLiteralToken :: TokenType -> Object -> State ScannerState ()
+addLiteralToken token object = modify $ scannerAddLiteralToken token object 
+
+scannerAddLiteralToken :: TokenType -> Object -> ScannerState -> ScannerState
+scannerAddLiteralToken tokenType object ScannerState {source=source, tokens=tokens} = ScannerState {source=source, tokens=token : tokens}
+    where token = Token {getType=tokenType, getLexeme="", getObject=object, getLineNumber= -1}
+