32 lines
1.1 KiB
Haskell
32 lines
1.1 KiB
Haskell
module Lexer where
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data Token = Plus
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| Minus
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| Multiply
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| Divide
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| Integer Int
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| LBrace
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| RBrace
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deriving Show
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lex :: String -> [Token]
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lex source = reverse (lex' source [] (length source))
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lex' :: String -> [Token] -> Int -> [Token]
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lex' "" tokens _ = tokens
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lex' (' ':xs) tokens orgLength = lex' xs tokens orgLength
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lex' (x:xs) tokens orgLength = case x of
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'+' -> lex' xs (Plus:tokens) orgLength
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'-' -> lex' xs (Minus:tokens) orgLength
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'*' -> lex' xs (Multiply:tokens) orgLength
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'/' -> lex' xs (Divide:tokens) orgLength
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'(' -> lex' xs (LBrace:tokens) orgLength
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')' -> lex' xs (RBrace:tokens) orgLength
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_ -> lexNumbers (x:xs) tokens orgLength
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lexNumbers :: String -> [Token] -> Int -> [Token]
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lexNumbers (x:xs) tokens orgLength
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| isDigit x = lex' (dropWhile isDigit (x:xs)) ((Integer(read (takeWhile isDigit (x:xs))::Int)):tokens) orgLength
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| otherwise = error $ "Syntax error: " ++ [x] ++ " (" ++ show (orgLength - (length (x:xs))) ++ ")"
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isDigit x = x `elem` "0123456789"
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