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-- MIT License, Copyright (c) 2024 Marvin Borner
{-# LANGUAGE OverloadedStrings #-}
module Language.Mili.Parser
( parseProgram
) where
import Control.Monad ( void )
import Control.Monad.State
import Data.Functor ( ($>) )
import Data.HashMap.Strict ( HashMap )
import qualified Data.HashMap.Strict as M
import Data.Mili ( Nat(..)
, Term(..)
, shift
)
import Data.Text ( Text )
import qualified Data.Text as T
import Data.Void
import Prelude hiding ( abs
, min
)
import Text.Megaparsec hiding ( State )
import Text.Megaparsec.Char
import qualified Text.Megaparsec.Char.Lexer as L
type Parser = ParsecT Void Text (State ParserState)
data ParserState = PS
{ _map :: HashMap Text (Int, Term)
, _depth :: Int
}
-- | single line comment
lineComment :: Parser ()
lineComment = L.skipLineComment "--"
-- | multiline comment
blockComment :: Parser ()
blockComment = L.skipBlockComment "{-" "-}"
parens :: Parser a -> Parser a
parens = between (symbol "(") (symbol ")")
-- | space consumer including comments
spaceConsumer :: String -> Parser ()
spaceConsumer s = L.space (void $ oneOf s) lineComment blockComment
-- | multiple spaces with comments
spaces :: Parser ()
spaces = spaceConsumer (" \t" :: String)
-- | multiple spaces and newlines with comments
anySpaces :: Parser ()
anySpaces = spaceConsumer (" \t\r\n" :: String)
-- | arbitrary symbol consumer
symbol :: Text -> Parser Text
symbol = string
-- | symbol consumer with arbitrary spaces behind
startSymbol :: Text -> Parser Text
startSymbol t = symbol t <* anySpaces
-- | natural number
nat :: Parser Nat
nat = natify <$> between (startSymbol "<") (symbol ">") L.decimal
where
natify 0 = Z
natify n = S $ Num $ natify (n - 1 :: Integer)
-- | convert de Bruijn indices to levels
toLevel :: Int -> Parser Term
toLevel n = do
PS { _depth = d } <- get
pure $ Lvl $ d - n - 1
-- | abstraction, entering increases the abstraction depth
abs :: Parser Term
abs = between (startSymbol "[")
(symbol "]")
(gets (Abs <$> _depth) <*> (inc *> block <* dec))
where
inc = modify $ \r@(PS { _depth = d }) -> r { _depth = d + 1 }
dec = modify $ \r@(PS { _depth = d }) -> r { _depth = d - 1 }
-- | de Bruijn index, parsed to de Bruijn level
idx :: Parser Term
idx = L.decimal >>= toLevel
-- | single number: <n> | S <term> | Z
num :: Parser Term
num =
(Num <$> nat)
<|> (Num <$> ((string "S" *> spaces $> S) <*> term))
<|> (Num <$> (string "Z" $> Z))
-- | unbounded iterator: REC (<term>, <nat>), <term>, <term>, <term>
rec :: Parser Term
rec = do
_ <- symbol "REC"
_ <- spaces
_ <- startSymbol "("
t1 <- term
_ <- spaces
_ <- startSymbol ","
t2 <- term
_ <- spaces
_ <- startSymbol ")"
_ <- startSymbol ","
u <- term
_ <- spaces
_ <- startSymbol ","
v <- term
_ <- spaces
_ <- startSymbol ","
w <- term
pure $ Rec (t1, t2) u v w
-- | single identifier, directly parsed to corresponding term
def :: Parser Term
def = do
name <- identifier
PS { _map = names, _depth = d1 } <- get
case M.lookup name names of
Just (d2, t) -> pure $ shift (d1 - d2) t
Nothing -> fail $ T.unpack name <> " is not in scope"
-- | single lambda term, potentially a left application fold of many
term :: Parser Term
term = try chain <|> once
where
once = abs <|> idx <|> num <|> rec <|> def <|> parens block
chain = foldl1 App <$> sepEndBy1 (try once) (char ' ')
-- | single identifier, a-z
identifier :: Parser Text
identifier = T.pack <$> some lowerChar
-- | single definition, <identifier> = <term>
definition :: Parser ()
definition = do
name <- identifier
_ <- spaces
_ <- startSymbol "="
_ <- spaces
body <- term
modify $ \r@(PS { _map = m, _depth = d }) ->
r { _map = M.insert name (d, body) m }
-- | many definitions, seperated by newline or semicolon
definitions :: Parser [()]
definitions = endBy (try definition) (oneOf (";\n" :: String) <* anySpaces)
-- | single "let..in" block: many definitions before a single term
block :: Parser Term
block = do
(PS { _map = m }) <- get -- backup
b <- definitions *> term
_ <- anySpaces
modify $ \r -> r { _map = m } -- restore
pure b
-- TODO: add preprocessor commands?
program :: Parser Term
program = block
parseProgram :: Text -> Either String Term
parseProgram s = prettify $ evalState
(runParserT (anySpaces *> program <* anySpaces <* eof) "" s)
PS { _map = M.empty, _depth = 0 }
where
prettify (Right t ) = Right t
prettify (Left err) = Left $ errorBundlePretty err
|
