really-bad-compiler-in-haskell/app/Parser/Expression.hs

module Parser.Expression (parseExpr, ParseResult) where

import Control.Monad.Combinators.Expr
import Data.Void (Void)
import Objects.Expression
import Text.Megaparsec as MP
import Text.Megaparsec.Char as C
import Text.Megaparsec.Char.Lexer as L

type Parser = Parsec Void String

lexemeParser :: Parser a -> Parser a
lexemeParser = L.lexeme C.space

symbolParser :: String -> Parser String
symbolParser = L.symbol C.space

intParser :: Parser Int
intParser = lexemeParser L.decimal

term :: Parser Expr
term = Lit <$> intParser

table :: [[Operator Parser Expr]]
table =
  [ [ binaryOp "*" Mul,
      binaryOp "/" Div
    ],
    [ binaryOp "+" Add,
      binaryOp "-" Sub
    ]
  ]

binaryOp name f = InfixL (f <$ symbolParser name)

expr :: Parser Expr
expr = makeExprParser term table

type ParseResult = Either (ParseErrorBundle String Void) Expr

parseExpr :: String -> ParseResult
parseExpr = MP.parse (C.space *> expr <* eof) ""

-- parseE = parseExpr