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{- A generic matcher.
-
- Can be used to check if a user-supplied condition,
- like "foo and ( bar or not baz )" matches. The condition must already
- be tokenized, and can contain arbitrary operations.
-
- If operations are not separated by and/or, they are defaulted to being
- anded together, so "foo bar baz" all must match.
-
- Is forgiving about misplaced closing parens, so "foo and (bar or baz"
- will be handled, as will "foo and ( bar or baz ) )"
-
- Copyright 2011 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Utility.Matcher (
Token(..),
Matcher,
generate,
match,
matchM,
matchesAny
) where
import Control.Monad
{- A Token can either be a single word, or an Operation of an arbitrary type. -}
data Token op = Token String | Operation op
deriving (Show, Eq)
data Matcher op = Any
| And (Matcher op) (Matcher op)
| Or (Matcher op) (Matcher op)
| Not (Matcher op)
| Op op
deriving (Show, Eq)
{- Converts a list of Tokens into a Matcher. -}
generate :: [Token op] -> Matcher op
generate ts = generate' Any ts
generate' :: Matcher op -> [Token op] -> Matcher op
generate' m [] = m
generate' m ts = uncurry generate' $ consume m ts
{- Consumes one or more Tokens, constructs a new Matcher,
- and returns unconsumed Tokens. -}
consume :: Matcher op -> [Token op] -> (Matcher op, [Token op])
consume m [] = (m, [])
consume m ((Operation o):ts) = (m `And` Op o, ts)
consume m ((Token t):ts)
| t == "and" = cont $ m `And` next
| t == "or" = cont $ m `Or` next
| t == "not" = cont $ m `And` (Not next)
| t == "(" = let (n, r) = consume next rest in (m `And` n, r)
| t == ")" = (m, ts)
| otherwise = error $ "unknown token " ++ t
where
(next, rest) = consume Any ts
cont v = (v, rest)
{- Checks if a Matcher matches, using a supplied function to check
- the value of Operations. -}
match :: (op -> v -> Bool) -> Matcher op -> v -> Bool
match a m v = go m
where
go Any = True
go (And m1 m2) = go m1 && go m2
go (Or m1 m2) = go m1 || go m2
go (Not m1) = not (go m1)
go (Op o) = a o v
{- Runs a monadic Matcher, where Operations are actions in the monad. -}
matchM :: Monad m => Matcher (v -> m Bool) -> v -> m Bool
matchM m v = go m
where
go Any = return True
go (And m1 m2) = liftM2 (&&) (go m1) (go m2)
go (Or m1 m2) = liftM2 (||) (go m1) (go m2)
go (Not m1) = liftM not (go m1)
go (Op o) = o v
{- Checks is a matcher contains no limits, and so (presumably) matches
- anything. Note that this only checks the trivial case; it is possible
- to construct matchers that match anything but are more complicated. -}
matchesAny :: Matcher a -> Bool
matchesAny Any = True
matchesAny _ = False
|
