@@ -1,6 +1,27 @@
1+-- | This module provides 'Context's which are used to expand expressions in
2+-- templates and allow for arbitrary customisation.
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.
8+-- For example, you can build a context that contains
10+-- > … <> functionField "concat" (const . concat) <> …
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:
15+-- > $partial(concat("templates/categories/", category))$
17+-- This will evaluate the @category@ field in the context, then prepend he path,
18+-- and include the referenced file as a template.
1--------------------------------------------------------------------------------
21--------------------------------------------------------------------------------
2{-# LANGUAGE CPP #-}
22{-# LANGUAGE CPP #-}
3{-# LANGUAGE ExistentialQuantification #-}
23{-# LANGUAGE ExistentialQuantification #-}
24+{-# LANGUAGE RankNTypes #-}
4module Hakyll.Web.Template.Context
25module Hakyll.Web.Template.Context
5 ( ContextField (..)
26 ( ContextField (..)
6 , Context (..)
27 , Context (..)
@@ -28,13 +49,17 @@ module Hakyll.Web.Template.Context
28 , teaserField
49 , teaserField
29 , teaserFieldWithSeparator
50 , teaserFieldWithSeparator
30 , missingField
51 , missingField
34--------------------------------------------------------------------------------
56--------------------------------------------------------------------------------
35import Control.Applicative (Alternative (..))
57import Control.Applicative (Alternative (..))
36import Control.Monad (msum)
58import Control.Monad (msum)
37−import Data.List (intercalate)
59+import Data.List (intercalate, tails)
60+#if MIN_VERSION_base(4,9,0)
61+import Data.Semigroup (Semigroup (..))
38import Data.Time.Clock (UTCTime (..))
63import Data.Time.Clock (UTCTime (..))
39import Data.Time.Format (formatTime)
64import Data.Time.Format (formatTime)
40import qualified Data.Time.Format as TF
65import qualified Data.Time.Format as TF
@@ -47,13 +72,16 @@ import Hakyll.Core.Metadata
47import Hakyll.Core.Provider
72import Hakyll.Core.Provider
48import Hakyll.Core.Util.String (needlePrefix, splitAll)
73import Hakyll.Core.Util.String (needlePrefix, splitAll)
49import Hakyll.Web.Html
74import Hakyll.Web.Html
75+import Prelude hiding (id)
50−import System.FilePath (splitDirectories, takeBaseName)
76+import System.FilePath (dropExtension, splitDirectories,
53--------------------------------------------------------------------------------
80--------------------------------------------------------------------------------
54-- | Mostly for internal usage
81-- | Mostly for internal usage
55data ContextField
82data ContextField
56− = StringField String
84+ | StringField String
57 | forall a. ListField (Context a) [Item a]
85 | forall a. ListField (Context a) [Item a]
@@ -78,71 +106,123 @@ newtype Context a = Context
80--------------------------------------------------------------------------------
108--------------------------------------------------------------------------------
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
115+instance Monoid (Context a) where
116+ mempty = missingField
81instance Monoid (Context a) where
119instance Monoid (Context a) where
82 mempty = missingField
120 mempty = missingField
83 mappend (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
121 mappend (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
86--------------------------------------------------------------------------------
125--------------------------------------------------------------------------------
87field' :: String -> (Item a -> Compiler ContextField) -> Context a
126field' :: String -> (Item a -> Compiler ContextField) -> Context a
88−field' key value = Context $ \k _ i -> if k == key then value i else empty
127+field' key value = Context $ \k _ i ->
130+ else noResult $ "Tried field " ++ key
91--------------------------------------------------------------------------------
133--------------------------------------------------------------------------------
92−-- | 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
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'.
94 :: String -- ^ Key
144 :: String -- ^ Key
95 -> (Item a -> Compiler String) -- ^ Function that constructs a value based
145 -> (Item a -> Compiler String) -- ^ Function that constructs a value based
96− -- on the item
146+ -- on the item (e.g. accessing metadata)
97 -> Context a
147 -> Context a
98field key value = field' key (fmap StringField . value)
148field key value = field' key (fmap StringField . value)
101--------------------------------------------------------------------------------
151--------------------------------------------------------------------------------
102-- | Creates a 'field' to use with the @$if()$@ template macro.
152-- | Creates a 'field' to use with the @$if()$@ template macro.
153+-- Attempting to substitute the field into the template will cause an error.
104 :: String
155 :: String
105 -> (Item a -> Bool)
156 -> (Item a -> Bool)
106 -> Context a
157 -> Context a
107−boolField name f = field name (\i -> if f i
158+boolField name f = field' name (\i -> if f i
108− then pure (error $ unwords ["no string value for bool field:",name])
159+ then return EmptyField
109− else empty)
160+ else noResult $ "Field " ++ name ++ " is false")
112--------------------------------------------------------------------------------
163--------------------------------------------------------------------------------
113−-- | Creates a 'field' that does not depend on the 'Item'
164+-- | Creates a 'field' that does not depend on the 'Item' but always yields
114−constField :: String -> String -> Context a
166+constField :: String -- ^ Key
167+ -> String -- ^ Value
115constField key = field key . const . return
169constField key = field key . const . return
118--------------------------------------------------------------------------------
172--------------------------------------------------------------------------------
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.
119listField :: String -> Context a -> Compiler [Item a] -> Context b
176listField :: String -> Context a -> Compiler [Item a] -> Context b
120listField key c xs = listFieldWith key c (const xs)
177listField key c xs = listFieldWith key c (const xs)
123--------------------------------------------------------------------------------
180--------------------------------------------------------------------------------
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
124listFieldWith
187listFieldWith
125 :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
188 :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
126listFieldWith key c f = field' key $ fmap (ListField c) . f
189listFieldWith key c f = field' key $ fmap (ListField c) . f
129--------------------------------------------------------------------------------
192--------------------------------------------------------------------------------
193+-- | Creates a variadic function field.
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
130−functionField :: String -> ([String] -> Item a -> Compiler String) -> Context a
198+ -> ([String] -> Item a -> Compiler String) -- ^ Function
131functionField name value = Context $ \k args i ->
200functionField name value = Context $ \k args i ->
132 if k == name
201 if k == name
133 then StringField <$> value args i
202 then StringField <$> value args i
134− else empty
203+ else noResult $ "Tried function field " ++ name
137--------------------------------------------------------------------------------
206--------------------------------------------------------------------------------
207+-- | Transform the respective string results of all fields in a context.
210+-- > mapContext (++"c") (constField "x" "a" <> constField "y" "b")
214+-- > constField "x" "ac" <> constField "y" "bc"
138mapContext :: (String -> String) -> Context a -> Context a
216mapContext :: (String -> String) -> Context a -> Context a
139mapContext f (Context c) = Context $ \k a i -> do
217mapContext f (Context c) = Context $ \k a i -> do
140 fld <- c k a i
218 fld <- c k a i
141 case fld of
219 case fld of
220+ EmptyField -> wrongType "boolField"
142 StringField str -> return $ StringField (f str)
221 StringField str -> return $ StringField (f str)
143− ListField _ _ -> fail $
222+ _ -> wrongType "ListField"
144− "Hakyll.Web.Template.Context.mapContext: " ++
224+ wrongType typ = fail $ "Hakyll.Web.Template.Context.mapContext: " ++
145− "can't map over a ListField!"
225+ "can't map over a " ++ typ ++ "!"
147--------------------------------------------------------------------------------
227--------------------------------------------------------------------------------
148-- | A context that allows snippet inclusion. In processed file, use as:
228-- | A context that allows snippet inclusion. In processed file, use as:
@@ -151,15 +231,15 @@ mapContext f (Context c) = Context $ \k a i -> do
151-- > $snippet("path/to/snippet/")$
231-- > $snippet("path/to/snippet/")$
154−-- The contents of the included file will not be interpolated.
234+-- The contents of the included file will not be interpolated like @partial@
156snippetField :: Context String
237snippetField :: Context String
157snippetField = functionField "snippet" f
238snippetField = functionField "snippet" f
159 f [contentsPath] _ = loadBody (fromFilePath contentsPath)
240 f [contentsPath] _ = loadBody (fromFilePath contentsPath)
160− f _ i = error $
241+ f [] _ = fail "No argument to function 'snippet()'"
161− "Too many arguments to function 'snippet()' in item " ++
242+ f _ _ = fail "Too many arguments to function 'snippet()'"
162− show (itemIdentifier i)
164--------------------------------------------------------------------------------
244--------------------------------------------------------------------------------
165-- | A context that contains (in that order)
245-- | A context that contains (in that order)
@@ -179,8 +259,7 @@ defaultContext =
179 metadataField `mappend`
259 metadataField `mappend`
180 urlField "url" `mappend`
260 urlField "url" `mappend`
181 pathField "path" `mappend`
261 pathField "path" `mappend`
182− titleField "title" `mappend`
262+ titleField "title"
186--------------------------------------------------------------------------------
265--------------------------------------------------------------------------------
@@ -198,15 +277,20 @@ bodyField key = field key $ return . itemBody
198-- | Map any field to its metadata value, if present
277-- | Map any field to its metadata value, if present
199metadataField :: Context a
278metadataField :: Context a
200metadataField = Context $ \k _ i -> do
279metadataField = Context $ \k _ i -> do
201− value <- getMetadataField (itemIdentifier i) k
280+ let id = itemIdentifier i
281+ empty' = noResult $ "No '" ++ k ++ "' field in metadata " ++
282+ "of item " ++ show id
283+ value <- getMetadataField id k
202− maybe empty (return . StringField) value
284+ maybe empty' (return . StringField) value
205--------------------------------------------------------------------------------
287--------------------------------------------------------------------------------
206-- | Absolute url to the resulting item
288-- | Absolute url to the resulting item
207urlField :: String -> Context a
289urlField :: String -> Context a
208−urlField key = field key $
290+urlField key = field key $ \i -> do
291+ let id = itemIdentifier i
292+ empty' = fail $ "No route url found for item " ++ show id
209− fmap (maybe empty toUrl) . getRoute . itemIdentifier
293+ fmap (maybe empty' toUrl) $ getRoute id
212--------------------------------------------------------------------------------
296--------------------------------------------------------------------------------
@@ -257,6 +341,12 @@ titleField = mapContext takeBaseName . pathField
257-- that begins with @yyyy-mm-dd@ . For example:
341-- that begins with @yyyy-mm-dd@ . For example:
258-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
342-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
259-- In case of multiple matches, the rightmost one is used.
343-- In case of multiple matches, the rightmost one is used.
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.
261dateField :: String -- ^ Key in which the rendered date should be placed
351dateField :: String -- ^ Key in which the rendered date should be placed
262 -> String -- ^ Format to use on the date
352 -> String -- ^ Format to use on the date
@@ -267,7 +357,7 @@ dateField = dateFieldWith defaultTimeLocale
267--------------------------------------------------------------------------------
357--------------------------------------------------------------------------------
268-- | This is an extended version of 'dateField' that allows you to
358-- | This is an extended version of 'dateField' that allows you to
269-- specify a time locale that is used for outputting the date. For more
359-- specify a time locale that is used for outputting the date. For more
270−-- details, see 'dateField'.
360+-- details, see 'dateField' and 'formatTime'.
271dateFieldWith :: TimeLocale -- ^ Output time locale
361dateFieldWith :: TimeLocale -- ^ Output time locale
272 -> String -- ^ Destination key
362 -> String -- ^ Destination key
273 -> String -- ^ Format to use on the date
363 -> String -- ^ Format to use on the date
@@ -288,12 +378,13 @@ getItemUTC :: MonadMetadata m
288getItemUTC locale id' = do
378getItemUTC locale id' = do
289 metadata <- getMetadata id'
379 metadata <- getMetadata id'
290 let tryField k fmt = lookupString k metadata >>= parseTime' fmt
380 let tryField k fmt = lookupString k metadata >>= parseTime' fmt
291− paths = splitDirectories $ toFilePath id'
381+ paths = splitDirectories $ (dropExtension . toFilePath) id'
293 maybe empty' return $ msum $
383 maybe empty' return $ msum $
294 [tryField "published" fmt | fmt <- formats] ++
384 [tryField "published" fmt | fmt <- formats] ++
295 [tryField "date" fmt | fmt <- formats] ++
385 [tryField "date" fmt | fmt <- formats] ++
296− [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]
298 empty' = fail $ "Hakyll.Web.Template.Context.getItemUTC: " ++
389 empty' = fail $ "Hakyll.Web.Template.Context.getItemUTC: " ++
299 "could not parse time for " ++ show id'
390 "could not parse time for " ++ show id'
@@ -321,13 +412,16 @@ getItemModificationTime identifier = do
323--------------------------------------------------------------------------------
414--------------------------------------------------------------------------------
415+-- | Creates a field with the last modification date of the underlying item.
324modificationTimeField :: String -- ^ Key
416modificationTimeField :: String -- ^ Key
325 -> String -- ^ Format
417 -> String -- ^ Format
326− -> Context a -- ^ Resuting context
418+ -> Context a -- ^ Resulting context
327modificationTimeField = modificationTimeFieldWith defaultTimeLocale
419modificationTimeField = modificationTimeFieldWith defaultTimeLocale
330--------------------------------------------------------------------------------
422--------------------------------------------------------------------------------
423+-- | Creates a field with the last modification date of the underlying item
424+-- in a custom localisation format (see 'formatTime').
331modificationTimeFieldWith :: TimeLocale -- ^ Time output locale
425modificationTimeFieldWith :: TimeLocale -- ^ Time output locale
332 -> String -- ^ Key
426 -> String -- ^ Key
333 -> String -- ^ Format
427 -> String -- ^ Format
@@ -366,10 +460,11 @@ teaserFieldWithSeparator separator key snapshot = field key $ \item -> do
368--------------------------------------------------------------------------------
462--------------------------------------------------------------------------------
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.
369missingField :: Context a
465missingField :: Context a
370−missingField = Context $ \k _ i -> fail $
466+missingField = Context $ \k _ _ -> noResult $
371− "Missing field $" ++ k ++ "$ in context for item " ++
467+ "Missing field '" ++ k ++ "' in context"
372− show (itemIdentifier i)
374parseTimeM :: Bool -> TimeLocale -> String -> String -> Maybe UTCTime
469parseTimeM :: Bool -> TimeLocale -> String -> String -> Maybe UTCTime
375#if MIN_VERSION_time(1,5,0)
470#if MIN_VERSION_time(1,5,0)
@@ -377,3 +472,10 @@ parseTimeM = TF.parseTimeM
378parseTimeM _ = TF.parseTime
473parseTimeM _ = TF.parseTime
476+--------------------------------------------------------------------------------
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