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Diffstat (limited to 'src/Text/Hakyll/Internal/Template.hs')
-rw-r--r-- | src/Text/Hakyll/Internal/Template.hs | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/src/Text/Hakyll/Internal/Template.hs b/src/Text/Hakyll/Internal/Template.hs new file mode 100644 index 0000000..41d279c --- /dev/null +++ b/src/Text/Hakyll/Internal/Template.hs @@ -0,0 +1,86 @@ +module Text.Hakyll.Internal.Template + ( Template + , fromString + , readTemplate + , substitute + , regularSubstitute + , finalSubstitute + ) where + +import qualified Data.Map as M +import Data.List (isPrefixOf) +import Data.Char (isAlphaNum) +import Data.Binary +import Control.Monad (liftM, liftM2) +import Data.Maybe (fromMaybe) +import System.FilePath ((</>)) +import Control.Monad.Reader (liftIO) + +import Text.Hakyll.Hakyll (Hakyll) +import Text.Hakyll.Context (Context) +import Text.Hakyll.Internal.Cache + +data Template = Chunk String Template + | Identifier String Template + | EscapeCharacter Template + | End + deriving (Show, Read) + +fromString :: String -> Template +fromString [] = End +fromString string + | "$$" `isPrefixOf` string = EscapeCharacter (fromString $ tail tail') + | "$" `isPrefixOf` string = let (key, rest) = span isAlphaNum tail' + in Identifier key (fromString rest) + | otherwise = let (chunk, rest) = break (== '$') string + in Chunk chunk (fromString rest) + where + tail' = tail string + +readTemplate :: FilePath -> Hakyll Template +readTemplate path = do + isCacheMoreRecent' <- isCacheMoreRecent fileName [path] + if isCacheMoreRecent' then getFromCache fileName + else do content <- liftIO $ readFile path + let template = fromString content + storeInCache template fileName + return template + where + fileName = "templates" </> path + +-- | Substitutes @$identifiers@ in the given "Template" by values from the given +-- "Context". When a key is not found, it is left as it is. You can specify +-- the characters used to replace escaped dollars (@$$@) here. +substitute :: String -> Template -> Context -> String +substitute escaper (Chunk chunk template) context = + chunk ++ substitute escaper template context +substitute escaper (Identifier key template) context = + replacement ++ substitute escaper template context + where + replacement = fromMaybe ('$' : key) $ M.lookup key context +substitute escaper (EscapeCharacter template) context = + escaper ++ substitute escaper template context +substitute _ End _ = [] + +-- | "substitute" for use during a chain. This will leave escaped characters as +-- they are. +regularSubstitute :: Template -> Context -> String +regularSubstitute = substitute "$$" + +-- | "substitute" for the end of a chain (just before writing). This renders +-- escaped characters. +finalSubstitute :: Template -> Context -> String +finalSubstitute = substitute "$" + +instance Binary Template where + put (Chunk string template) = put (0 :: Word8) >> put string >> put template + put (Identifier key template) = put (1 :: Word8) >> put key >> put template + put (EscapeCharacter template) = put (2 :: Word8) >> put template + put (End) = put (3 :: Word8) + + get = do tag <- getWord8 + case tag of 0 -> liftM2 Chunk get get + 1 -> liftM2 Identifier get get + 2 -> liftM EscapeCharacter get + 3 -> return End + _ -> error "Error reading template" |