module Language.Lambda.Parser where
import Text.Parsec
import Language.Lambda.AST
import Data.Functor.Identity
import Data.List
type M = Identity
type Output = Expr
top_expr :: ParsecT String u M Output
top_expr = do
spaces
e <- parse_expr
spaces
eof
return e
parse_expr :: ParsecT String u M Output
parse_expr = try parse_aexpr
<|> try parse_lambda
parse_aexpr :: ParsecT String u M Output
parse_aexpr = try parse_app
<|> try parse_atom
parse_lambda :: ParsecT String u M Output
parse_lambda = do
_ <- char '\\'
sym <- parse_sym <?> "lambda argument"
_ <- char '.'
expr <- parse_expr <?> "lambda expression"
return $ Lam sym expr
parse_app :: ParsecT String u M Output
parse_app = do
expr_0 <- parse_atom <?> "first apply argument"
spaces
as <- sepBy1 parse_atom spaces <?> "other apply arguments"
return $ foldl' App expr_0 as
parse_atom :: ParsecT String u M Output
parse_atom = try (parens' parse_expr)
<|> try parse_var
parse_var :: ParsecT String u M Output
parse_var = do
spaces
sym <- parse_sym <?> "Var symbol"
return $ Var sym
parse_sym :: ParsecT String u M String
parse_sym = many1 (alphaNum <|> char '_') <?> "symbol"
parens' :: Stream s m Char => ParsecT s u m b -> ParsecT s u m b
parens' p = do
_ <- char '('
e <- p
_ <- char ')'
return e