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module Expr (parseE, Expr(..)) where
import Text.Parsec
import Text.Parsec.Language
import Text.Parsec.Token
import Text.Parsec.Expr
import qualified Data.Functor.Identity
data Expr = Plus Expr Expr
| Negate Expr
| Minus Expr Expr
| Times Expr Expr
| Div Expr Expr
| EInt Integer
| EFloat Double
| E
| Pi
| Log Expr
| Sin Expr
| Cos Expr
| Sqrt Expr
tokenParser :: TokenParser st
tokenParser = haskell
parseNumber :: Parsec String u Expr
parseNumber = do n <- naturalOrFloat tokenParser
case n of
Left i -> return (EInt i)
Right d -> return (EFloat d)
tokenS :: String -> Parsec String u ()
tokenS s = () <$ try (symbol tokenParser s)
inner :: Parsec String u Expr
inner = parseNumber <|> E <$ tokenS "e" <|> Pi <$ tokenS "pi" <|> parens tokenParser parseExpr
binary :: String -> (a -> a -> a) -> Assoc
-> Operator String u Data.Functor.Identity.Identity a
binary name fun assoc =
Infix (fun <$ tokenS name) assoc
prefix :: String -> (a -> a)
-> Operator String u Data.Functor.Identity.Identity a
prefix name fun = Prefix (fun <$ tokenS name)
table :: [[Operator String u Data.Functor.Identity.Identity Expr]]
table = [ [ prefix "log" Log, prefix "sin" Sin, prefix "cos" Cos, prefix "sqrt" Sqrt ]
, [ prefix "-" Negate ]
, [ binary "*" Times AssocLeft
, binary "/" Div AssocLeft
]
, [ binary "+" Plus AssocLeft
, binary "-" Minus AssocLeft
]
]
parseExpr :: Parsec String u Expr
parseExpr = buildExpressionParser table inner
parser :: Parsec String u Expr
parser = do whiteSpace tokenParser
parseExpr
parseE :: String -> Either ParseError Expr
parseE s = parse parser "" s
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