88 lines
2.4 KiB
Haskell
88 lines
2.4 KiB
Haskell
{- A generic matcher.
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-
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- Can be used to check if a user-supplied condition,
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- like "foo and ( bar or not baz )" matches. The condition must already
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- be tokenized, and can contain arbitrary operations.
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-
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- If operations are not separated by and/or, they are defaulted to being
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- anded together, so "foo bar baz" all must match.
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-
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- Is forgiving about misplaced closing parens, so "foo and (bar or baz"
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- will be handled, as will "foo and ( bar or baz ) )"
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-
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- Copyright 2011 Joey Hess <joey@kitenet.net>
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-
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- Licensed under the GNU GPL version 3 or higher.
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-}
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module Matcher (
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Operation(..),
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Token(..),
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toMatcher,
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match,
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runMatch
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) where
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import Control.Monad
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{- An Operation is a command and some parameters. -}
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data Operation = Operation String [String]
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deriving (Show, Eq)
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{- A Token can either be a single word, or an Operation. -}
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data Token = Token String | TokenOp Operation
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deriving (Show, Eq)
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data Matcher = Any
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| And Matcher Matcher
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| Or Matcher Matcher
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| Not Matcher
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| Op Operation
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deriving (Show, Eq)
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{- Converts a list of Tokens into a Matcher. -}
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toMatcher :: [Token] -> Matcher
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toMatcher ts = toMatcher' Any ts
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toMatcher' :: Matcher -> [Token] -> Matcher
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toMatcher' m [] = m
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toMatcher' m ts = toMatcher' m' rest
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where
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(m', rest) = consume m ts
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{- Consumes one or more tokens, constructs a new Matcher,
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- and returns unconsumed tokens. -}
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consume :: Matcher -> [Token] -> (Matcher, [Token])
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consume m [] = (m, [])
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consume m ((TokenOp o):ts) = (m `And` Op o, ts)
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consume m ((Token t):ts)
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| t == "and" = cont $ m `And` next
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| t == "or" = cont $ m `Or` next
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| t == "not" = cont $ m `And` (Not next)
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| t == "(" = let (n, r) = consume next rest in (m `And` n, r)
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| t == ")" = (m, ts)
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| otherwise = (m, ts) -- ignore unknown token
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where
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(next, rest) = consume Any ts
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cont v = (v, rest)
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{- Checks if a Matcher matches, using a supplied function to check
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- the value of Operations. -}
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match :: (Operation -> Bool) -> Matcher -> Bool
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match a = go
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where
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go Any = True
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go (And m1 m2) = go m1 && go m2
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go (Or m1 m2) = go m1 || go m2
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go (Not m1) = not (go m1)
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go (Op v) = a v
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{- Runs a Matcher in an arbitrary monadic contex, using a supplied
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- action to evaluate Operations. -}
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runMatch :: Monad m => (Operation -> m Bool) -> Matcher -> m Bool
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runMatch a = go
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where
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go Any = return True
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go (And m1 m2) = liftM2 (&&) (go m1) (go m2)
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go (Or m1 m2) = liftM2 (||) (go m1) (go m2)
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go (Not m1) = liftM not (go m1)
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go (Op v) = a v
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