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|
-- | Module providing pattern matching and capturing on 'Identifier's.
--
-- A very simple pattern could be, for example, @foo\/bar@. This pattern will
-- only match the exact @foo\/bar@ identifier.
--
-- To match more than one identifier, there are different captures that one can
-- use:
--
-- * @*@: matches exactly one element of an identifier;
--
-- * @**@: matches one or more elements of an identifier.
--
-- Some examples:
--
-- * @foo\/*@ will match @foo\/bar@ and @foo\/foo@, but not @foo\/bar\/qux@ nor
-- @foo@;
--
-- * @**@ will match any non-empty identifier;
--
-- * @foo\/**@ will match @foo\/bar@ and @foo\/bar\/qux@, but not @bar\/foo@ nor
-- @foo@;
--
-- A small warning: patterns are not globs. Using @foo\/*.markdown@ will not do
-- what you probably intended, as it will only match the file which is literally
-- called @foo\/*.markdown@. Remember that these captures only work on elements
-- of identifiers as a whole; not on parts of these elements.
--
-- Furthermore, the 'match' function allows the user to get access to the
-- elements captured by the capture elements in the pattern.
--
module Hakyll.Core.Identifier.Pattern
( Pattern
, parsePattern
, match
, doesMatch
, matches
, fromCapture
, fromCaptures
) where
import Data.List (intercalate)
import Control.Monad (msum)
import Data.Maybe (isJust)
import Data.Monoid (mempty, mappend)
import GHC.Exts (IsString, fromString)
import Hakyll.Core.Identifier
-- | One base element of a pattern
--
data PatternComponent = CaptureOne
| CaptureMany
| Literal String
deriving (Eq)
instance Show PatternComponent where
show CaptureOne = "*"
show CaptureMany = "**"
show (Literal s) = s
-- | Type that allows matching on identifiers
--
newtype Pattern = Pattern {unPattern :: [PatternComponent]}
deriving (Eq)
instance Show Pattern where
show = intercalate "/" . map show . unPattern
instance IsString Pattern where
fromString = parsePattern
-- | Parse a pattern from a string
--
parsePattern :: String -> Pattern
parsePattern = Pattern . map toPattern . unIdentifier . parseIdentifier
where
toPattern x | x == "*" = CaptureOne
| x == "**" = CaptureMany
| otherwise = Literal x
-- | Match an identifier against a pattern, generating a list of captures
--
match :: Pattern -> Identifier -> Maybe [Identifier]
match (Pattern p) (Identifier i) = fmap (map Identifier) $ match' p i
-- | Check if an identifier matches a pattern
--
doesMatch :: Pattern -> Identifier -> Bool
doesMatch p = isJust . match p
-- | Given a list of identifiers, retain only those who match the given pattern
--
matches :: Pattern -> [Identifier] -> [Identifier]
matches p = filter (doesMatch p)
-- | Split a list at every possible point, generate a list of (init, tail) cases
--
splits :: [a] -> [([a], [a])]
splits ls = reverse $ splits' [] ls
where
splits' lx ly = (lx, ly) : case ly of
[] -> []
(y : ys) -> splits' (lx ++ [y]) ys
-- | Internal verion of 'match'
--
match' :: [PatternComponent] -> [String] -> Maybe [[String]]
match' [] [] = Just [] -- An empty match
match' [] _ = Nothing -- No match
match' _ [] = Nothing -- No match
match' (m : ms) (s : ss) = case m of
-- Take one string and one literal, fail on mismatch
Literal l -> if s == l then match' ms ss else Nothing
-- Take one string and one capture
CaptureOne -> fmap ([s] :) $ match' ms ss
-- Take one string, and one or many captures
CaptureMany ->
let take' (i, t) = fmap (i :) $ match' ms t
in msum $ map take' $ splits (s : ss)
-- | Create an identifier from a pattern by filling in the captures with a given
-- string
--
fromCapture :: Pattern -> Identifier -> Identifier
fromCapture pattern = fromCaptures pattern . repeat
-- | Create an identifier from a pattern by filling in the captures with the
-- given list of strings
--
fromCaptures :: Pattern -> [Identifier] -> Identifier
fromCaptures (Pattern []) _ = mempty
fromCaptures (Pattern (m : ms)) [] = case m of
Literal l -> Identifier [l] `mappend` fromCaptures (Pattern ms) []
_ -> error $ "Hakyll.Core.Identifier.Pattern.fromCaptures: "
++ "identifier list exhausted"
fromCaptures (Pattern (m : ms)) ids@(i : is) = case m of
Literal l -> Identifier [l] `mappend` fromCaptures (Pattern ms) ids
_ -> i `mappend` fromCaptures (Pattern ms) is
|
