@@ -1,6 +1,27 @@
1+-- | This module provides 'Context's which are used to expand expressions in
2+-- templates and allow for arbitrary customisation.
3+--
4+-- 'Template's define a small expression DSL which consists of strings,
5+-- identifiers and function application. There is no type system, every value is
6+-- a string and on the top level they get substituted verbatim into the page.
7+--
8+-- For example, you can build a context that contains
9+--
10+-- > … <> functionField "concat" (const . concat) <> …
11+--
12+-- which will allow you to use the @concat@ identifier as a function that takes
13+-- arbitrarily many stings and concatenates them to a new string:
14+--
15+-- > $partial(concat("templates/categories/", category))$
16+--
17+-- This will evaluate the @category@ field in the context, then prepend he path,
18+-- and include the referenced file as a template.
19+
20+
121--------------------------------------------------------------------------------
222{-# LANGUAGE CPP #-}
323{-# LANGUAGE ExistentialQuantification #-}
24+{-# LANGUAGE RankNTypes #-}
425module Hakyll.Web.Template.Context
526 ( ContextField (..)
627 , Context (..)
@@ -18,30 +39,31 @@ module Hakyll.Web.Template.Context
1839 , urlField
1940 , pathField
2041 , titleField
42+ , snippetField
2143 , dateField
2244 , dateFieldWith
2345 , getItemUTC
46+ , getItemModificationTime
2447 , modificationTimeField
2548 , modificationTimeFieldWith
2649 , teaserField
2750 , teaserFieldWithSeparator
2851 , missingField
52+ , bindItem
2953 ) where
3054
3155
3256--------------------------------------------------------------------------------
33−import Control.Applicative (Alternative (..), pure, (<$>))
57+import Control.Applicative (Alternative (..))
3458import Control.Monad (msum)
35−import Data.List (intercalate)
36−import qualified Data.Map as M
37−import Data.Monoid (Monoid (..))
59+import Data.List (intercalate, tails)
60+#if MIN_VERSION_base(4,9,0)
61+import Data.Semigroup (Semigroup (..))
62+#endif
3863import Data.Time.Clock (UTCTime (..))
3964import Data.Time.Format (formatTime)
4065import qualified Data.Time.Format as TF
4166import Data.Time.Locale.Compat (TimeLocale, defaultTimeLocale)
42−import System.FilePath (splitDirectories, takeBaseName)
43−
44−--------------------------------------------------------------------------------
4567import Hakyll.Core.Compiler
4668import Hakyll.Core.Compiler.Internal
4769import Hakyll.Core.Identifier
@@ -50,12 +72,16 @@ import Hakyll.Core.Metadata
5072import Hakyll.Core.Provider
5173import Hakyll.Core.Util.String (needlePrefix, splitAll)
5274import Hakyll.Web.Html
75+import Prelude hiding (id)
76+import System.FilePath (dropExtension, splitDirectories,
77+ takeBaseName)
5378
5479
5580--------------------------------------------------------------------------------
5681-- | Mostly for internal usage
5782data ContextField
58− = StringField String
83+ = EmptyField
84+ | StringField String
5985 | forall a. ListField (Context a) [Item a]
6086
6187
@@ -80,72 +106,140 @@ newtype Context a = Context
80106
81107
82108--------------------------------------------------------------------------------
109+-- | Tries to find a key in the left context,
110+-- or when that fails in the right context.
111+#if MIN_VERSION_base(4,9,0)
112+instance Semigroup (Context a) where
113+ (<>) (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
114+
115+instance Monoid (Context a) where
116+ mempty = missingField
117+ mappend = (<>)
118+#else
83119instance Monoid (Context a) where
84120 mempty = missingField
85121 mappend (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
122+#endif
86123
87124
88125--------------------------------------------------------------------------------
89126field' :: String -> (Item a -> Compiler ContextField) -> Context a
90−field' key value = Context $ \k _ i -> if k == key then value i else empty
127+field' key value = Context $ \k _ i ->
128+ if k == key
129+ then value i
130+ else noResult $ "Tried field " ++ key
91131
92132
93133--------------------------------------------------------------------------------
94−-- | Constructs a new field in the 'Context.'
134+-- | Constructs a new field for a 'Context'.
135+-- If the key matches, the compiler is run and its result is substituted in the
136+-- template.
137+--
138+-- If the compiler fails, the field will be considered non-existent
139+-- in an @$if()$@ macro or ultimately break the template application
140+-- (unless the key is found in another context when using '<>').
141+-- Use 'empty' or 'noResult' for intentional failures of fields used in
142+-- @$if()$@, to distinguish them from exceptions thrown with 'fail'.
95143field
96144 :: String -- ^ Key
97145 -> (Item a -> Compiler String) -- ^ Function that constructs a value based
98− -- on the item
146+ -- on the item (e.g. accessing metadata)
99147 -> Context a
100148field key value = field' key (fmap StringField . value)
101149
102150
103151--------------------------------------------------------------------------------
104152-- | Creates a 'field' to use with the @$if()$@ template macro.
153+-- Attempting to substitute the field into the template will cause an error.
105154boolField
106155 :: String
107156 -> (Item a -> Bool)
108157 -> Context a
109−boolField name f = field name (\i -> if f i
110− then pure (error $ unwords ["no string value for bool field:",name])
111− else empty)
158+boolField name f = field' name (\i -> if f i
159+ then return EmptyField
160+ else noResult $ "Field " ++ name ++ " is false")
112161
113162
114163--------------------------------------------------------------------------------
115−-- | Creates a 'field' that does not depend on the 'Item'
116−constField :: String -> String -> Context a
164+-- | Creates a 'field' that does not depend on the 'Item' but always yields
165+-- the same string
166+constField :: String -- ^ Key
167+ -> String -- ^ Value
168+ -> Context a
117169constField key = field key . const . return
118170
119171
120172--------------------------------------------------------------------------------
173+-- | Creates a list field to be consumed by a @$for(…)$@ expression.
174+-- The compiler returns multiple items which are rendered in the loop body
175+-- with the supplied context.
121176listField :: String -> Context a -> Compiler [Item a] -> Context b
122177listField key c xs = listFieldWith key c (const xs)
123178
124179
125180--------------------------------------------------------------------------------
181+-- | Produces a new 'Context' which has list field 'key'. All fields from
182+-- 'c' are also accessible from the produced context.
183+-- Be careful when doing @listFieldWith k ca f <> cb@ as any fields in @ca@
184+-- will override fields in @cb@ with the same name.
185+-- Creates a list field like 'listField', but supplies the current page
186+-- to the compiler.
126187listFieldWith
127188 :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
128189listFieldWith key c f = field' key $ fmap (ListField c) . f
129190
130191
131192--------------------------------------------------------------------------------
132−functionField :: String -> ([String] -> Item a -> Compiler String) -> Context a
193+-- | Creates a variadic function field.
194+--
195+-- The function will be called with the dynamically evaluated string arguments
196+-- from the template as well as the page that is currently rendered.
197+functionField :: String -- ^ Key
198+ -> ([String] -> Item a -> Compiler String) -- ^ Function
199+ -> Context a
133200functionField name value = Context $ \k args i ->
134201 if k == name
135202 then StringField <$> value args i
136− else empty
203+ else noResult $ "Tried function field " ++ name
137204
138205
139206--------------------------------------------------------------------------------
207+-- | Transform the respective string results of all fields in a context.
208+-- For example,
209+--
210+-- > mapContext (++"c") (constField "x" "a" <> constField "y" "b")
211+--
212+-- is equivalent to
213+--
214+-- > constField "x" "ac" <> constField "y" "bc"
215+--
140216mapContext :: (String -> String) -> Context a -> Context a
141217mapContext f (Context c) = Context $ \k a i -> do
142218 fld <- c k a i
143219 case fld of
220+ EmptyField -> wrongType "boolField"
144221 StringField str -> return $ StringField (f str)
145− ListField _ _ -> fail $
146− "Hakyll.Web.Template.Context.mapContext: " ++
147− "can't map over a ListField!"
222+ _ -> wrongType "ListField"
223+ where
224+ wrongType typ = fail $ "Hakyll.Web.Template.Context.mapContext: " ++
225+ "can't map over a " ++ typ ++ "!"
148226
227+--------------------------------------------------------------------------------
228+-- | A context that allows snippet inclusion. In processed file, use as:
229+--
230+-- > ...
231+-- > $snippet("path/to/snippet/")$
232+-- > ...
233+--
234+-- The contents of the included file will not be interpolated like @partial@
235+-- does it.
236+--
237+snippetField :: Context String
238+snippetField = functionField "snippet" f
239+ where
240+ f [contentsPath] _ = loadBody (fromFilePath contentsPath)
241+ f [] _ = fail "No argument to function 'snippet()'"
242+ f _ _ = fail "Too many arguments to function 'snippet()'"
149243
150244--------------------------------------------------------------------------------
151245-- | A context that contains (in that order)
@@ -165,8 +259,7 @@ defaultContext =
165259 metadataField `mappend`
166260 urlField "url" `mappend`
167261 pathField "path" `mappend`
168− titleField "title" `mappend`
169− missingField
262+ titleField "title"
170263
171264
172265--------------------------------------------------------------------------------
@@ -184,15 +277,20 @@ bodyField key = field key $ return . itemBody
184277-- | Map any field to its metadata value, if present
185278metadataField :: Context a
186279metadataField = Context $ \k _ i -> do
187− value <- getMetadataField (itemIdentifier i) k
188− maybe empty (return . StringField) value
280+ let id = itemIdentifier i
281+ empty' = noResult $ "No '" ++ k ++ "' field in metadata " ++
282+ "of item " ++ show id
283+ value <- getMetadataField id k
284+ maybe empty' (return . StringField) value
189285
190286
191287--------------------------------------------------------------------------------
192288-- | Absolute url to the resulting item
193289urlField :: String -> Context a
194−urlField key = field key $
195− fmap (maybe empty toUrl) . getRoute . itemIdentifier
290+urlField key = field key $ \i -> do
291+ let id = itemIdentifier i
292+ empty' = fail $ "No route url found for item " ++ show id
293+ fmap (maybe empty' toUrl) $ getRoute id
196294
197295
198296--------------------------------------------------------------------------------
@@ -243,6 +341,12 @@ titleField = mapContext takeBaseName . pathField
243341-- that begins with @yyyy-mm-dd@ . For example:
244342-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
245343-- In case of multiple matches, the rightmost one is used.
344+--
345+-- As another alternative, if none of the above matches, and the file has a
346+-- path which contains nested directories specifying a date, then that date
347+-- will be used. In other words, if the path is of the form
348+-- @**//yyyy//mm//dd//**//main.extension@ .
349+-- As above, in case of multiple matches, the rightmost one is used.
246350
247351dateField :: String -- ^ Key in which the rendered date should be placed
248352 -> String -- ^ Format to use on the date
@@ -253,7 +357,7 @@ dateField = dateFieldWith defaultTimeLocale
253357--------------------------------------------------------------------------------
254358-- | This is an extended version of 'dateField' that allows you to
255359-- specify a time locale that is used for outputting the date. For more
256−-- details, see 'dateField'.
360+-- details, see 'dateField' and 'formatTime'.
257361dateFieldWith :: TimeLocale -- ^ Output time locale
258362 -> String -- ^ Destination key
259363 -> String -- ^ Format to use on the date
@@ -273,13 +377,14 @@ getItemUTC :: MonadMetadata m
273377 -> m UTCTime -- ^ Parsed UTCTime
274378getItemUTC locale id' = do
275379 metadata <- getMetadata id'
276− let tryField k fmt = M.lookup k metadata >>= parseTime' fmt
277− paths = splitDirectories $ toFilePath id'
380+ let tryField k fmt = lookupString k metadata >>= parseTime' fmt
381+ paths = splitDirectories $ (dropExtension . toFilePath) id'
278382
279383 maybe empty' return $ msum $
280384 [tryField "published" fmt | fmt <- formats] ++
281385 [tryField "date" fmt | fmt <- formats] ++
282− [parseTime' "%Y-%m-%d" $ intercalate "-" $ take 3 $ splitAll "-" fnCand | fnCand <- reverse paths]
386+ [parseTime' "%Y-%m-%d" $ intercalate "-" $ take 3 $ splitAll "-" fnCand | fnCand <- reverse paths] ++
387+ [parseTime' "%Y-%m-%d" $ intercalate "-" $ fnCand | fnCand <- map (take 3) $ reverse . tails $ paths]
283388 where
284389 empty' = fail $ "Hakyll.Web.Template.Context.getItemUTC: " ++
285390 "could not parse time for " ++ show id'
@@ -296,20 +401,33 @@ getItemUTC locale id' = do
296401
297402
298403--------------------------------------------------------------------------------
404+-- | Get the time on which the actual file was last modified. This only works if
405+-- there actually is an underlying file, of couse.
406+getItemModificationTime
407+ :: Identifier
408+ -> Compiler UTCTime
409+getItemModificationTime identifier = do
410+ provider <- compilerProvider <$> compilerAsk
411+ return $ resourceModificationTime provider identifier
412+
413+
414+--------------------------------------------------------------------------------
415+-- | Creates a field with the last modification date of the underlying item.
299416modificationTimeField :: String -- ^ Key
300417 -> String -- ^ Format
301− -> Context a -- ^ Resuting context
418+ -> Context a -- ^ Resulting context
302419modificationTimeField = modificationTimeFieldWith defaultTimeLocale
303420
304421
305422--------------------------------------------------------------------------------
423+-- | Creates a field with the last modification date of the underlying item
424+-- in a custom localisation format (see 'formatTime').
306425modificationTimeFieldWith :: TimeLocale -- ^ Time output locale
307426 -> String -- ^ Key
308427 -> String -- ^ Format
309428 -> Context a -- ^ Resulting context
310429modificationTimeFieldWith locale key fmt = field key $ \i -> do
311− provider <- compilerProvider <$> compilerAsk
312− let mtime = resourceModificationTime provider $ itemIdentifier i
430+ mtime <- getItemModificationTime $ itemIdentifier i
313431 return $ formatTime locale fmt mtime
314432
315433
@@ -342,10 +460,11 @@ teaserFieldWithSeparator separator key snapshot = field key $ \item -> do
342460
343461
344462--------------------------------------------------------------------------------
463+-- | Constantly reports any field as missing. Mostly for internal usage,
464+-- it is the last choice in every context used in a template application.
345465missingField :: Context a
346−missingField = Context $ \k _ i -> fail $
347− "Missing field $" ++ k ++ "$ in context for item " ++
348− show (itemIdentifier i)
466+missingField = Context $ \k _ _ -> noResult $
467+ "Missing field '" ++ k ++ "' in context"
349468
350469parseTimeM :: Bool -> TimeLocale -> String -> String -> Maybe UTCTime
351470#if MIN_VERSION_time(1,5,0)
@@ -353,3 +472,10 @@ parseTimeM = TF.parseTimeM
353472#else
354473parseTimeM _ = TF.parseTime
355474#endif
475+
476+--------------------------------------------------------------------------------
477+
478+-- | Binds an 'Item' to a given 'Context', allowing it to be combined with any
479+-- other 'Context' of any type.
480+bindItem :: Context a -> Item a -> forall b. Context b
481+bindItem (Context ctx) ia = Context $ \k args _ -> ctx k args ia