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module Parser
( parseProgram
) where
import Text.Parsec
import Text.Parsec.String (Parser)
import Core
lexeme :: Parser a -> Parser a
lexeme p = p <* spaces
symbol :: String -> Parser String
symbol = lexeme . string
keyword :: String -> Parser ()
keyword s = try (string s *> notFollowedBy alphaNum) *> spaces
parens :: Parser a -> Parser a
parens = between (symbol "(") (symbol ")")
parseTerm :: Parser Term
parseTerm = parseIf
<|> parseSucc
<|> parsePred
<|> parseIsZero
<|> parseTrue
<|> parseFalse
<|> parseZero
<|> parens parseTerm
parseTrue :: Parser Term
parseTrue = TmTrue <$ keyword "true"
parseFalse :: Parser Term
parseFalse = TmFalse <$ keyword "false"
parseZero :: Parser Term
parseZero = TmZero <$ symbol "0"
parseIf :: Parser Term
parseIf = do
keyword "if"
t1 <- parseTerm
keyword "then"
t2 <- parseTerm
keyword "else"
t3 <- parseTerm
return $ TmIf t1 t2 t3
parseSucc :: Parser Term
parseSucc = do
keyword "succ"
t <- parseTerm
return $ TmSucc t
parsePred :: Parser Term
parsePred = do
keyword "pred"
t <- parseTerm
return $ TmPred t
parseIsZero :: Parser Term
parseIsZero = do
keyword "iszero"
t <- parseTerm
return $ TmIsZero t
parseProgram :: Parser Term
parseProgram = spaces *> parseTerm <* eof
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