@@ -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 +49,14 @@ 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)
38#if MIN_VERSION_base(4,9,0)
60#if MIN_VERSION_base(4,9,0)
39import Data.Semigroup (Semigroup (..))
61import Data.Semigroup (Semigroup (..))
@@ -50,13 +72,16 @@ import Hakyll.Core.Metadata
50import Hakyll.Core.Provider
72import Hakyll.Core.Provider
51import Hakyll.Core.Util.String (needlePrefix, splitAll)
73import Hakyll.Core.Util.String (needlePrefix, splitAll)
52import Hakyll.Web.Html
74import Hakyll.Web.Html
75+import Prelude hiding (id)
53−import System.FilePath (splitDirectories, takeBaseName, dropExtension)
76+import System.FilePath (dropExtension, splitDirectories,
56--------------------------------------------------------------------------------
80--------------------------------------------------------------------------------
57-- | Mostly for internal usage
81-- | Mostly for internal usage
58data ContextField
82data ContextField
59− = StringField String
84+ | StringField String
60 | forall a. ListField (Context a) [Item a]
85 | forall a. ListField (Context a) [Item a]
@@ -81,6 +106,8 @@ newtype Context a = Context
83--------------------------------------------------------------------------------
108--------------------------------------------------------------------------------
109+-- | Tries to find a key in the left context,
110+-- or when that fails in the right context.
84#if MIN_VERSION_base(4,9,0)
111#if MIN_VERSION_base(4,9,0)
85instance Semigroup (Context a) where
112instance Semigroup (Context a) where
86 (<>) (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
113 (<>) (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
@@ -97,64 +124,105 @@ instance Monoid (Context a) where
98--------------------------------------------------------------------------------
125--------------------------------------------------------------------------------
99field' :: String -> (Item a -> Compiler ContextField) -> Context a
126field' :: String -> (Item a -> Compiler ContextField) -> Context a
100−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
103--------------------------------------------------------------------------------
133--------------------------------------------------------------------------------
104−-- | 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'.
106 :: String -- ^ Key
144 :: String -- ^ Key
107 -> (Item a -> Compiler String) -- ^ Function that constructs a value based
145 -> (Item a -> Compiler String) -- ^ Function that constructs a value based
108− -- on the item
146+ -- on the item (e.g. accessing metadata)
109 -> Context a
147 -> Context a
110field key value = field' key (fmap StringField . value)
148field key value = field' key (fmap StringField . value)
113--------------------------------------------------------------------------------
151--------------------------------------------------------------------------------
114-- | 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.
116 :: String
155 :: String
117 -> (Item a -> Bool)
156 -> (Item a -> Bool)
118 -> Context a
157 -> Context a
119−boolField name f = field name (\i -> if f i
158+boolField name f = field' name (\i -> if f i
120− then pure (error $ unwords ["no string value for bool field:",name])
159+ then return EmptyField
121− else empty)
160+ else noResult $ "Field " ++ name ++ " is false")
124--------------------------------------------------------------------------------
163--------------------------------------------------------------------------------
125−-- | Creates a 'field' that does not depend on the 'Item'
164+-- | Creates a 'field' that does not depend on the 'Item' but always yields
126−constField :: String -> String -> Context a
166+constField :: String -- ^ Key
167+ -> String -- ^ Value
127constField key = field key . const . return
169constField key = field key . const . return
130--------------------------------------------------------------------------------
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.
131listField :: String -> Context a -> Compiler [Item a] -> Context b
176listField :: String -> Context a -> Compiler [Item a] -> Context b
132listField key c xs = listFieldWith key c (const xs)
177listField key c xs = listFieldWith key c (const xs)
135--------------------------------------------------------------------------------
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
136listFieldWith
187listFieldWith
137 :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
188 :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
138listFieldWith key c f = field' key $ fmap (ListField c) . f
189listFieldWith key c f = field' key $ fmap (ListField c) . f
141--------------------------------------------------------------------------------
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
142−functionField :: String -> ([String] -> Item a -> Compiler String) -> Context a
198+ -> ([String] -> Item a -> Compiler String) -- ^ Function
143functionField name value = Context $ \k args i ->
200functionField name value = Context $ \k args i ->
144 if k == name
201 if k == name
145 then StringField <$> value args i
202 then StringField <$> value args i
146− else empty
203+ else noResult $ "Tried function field " ++ name
149--------------------------------------------------------------------------------
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"
150mapContext :: (String -> String) -> Context a -> Context a
216mapContext :: (String -> String) -> Context a -> Context a
151mapContext f (Context c) = Context $ \k a i -> do
217mapContext f (Context c) = Context $ \k a i -> do
152 fld <- c k a i
218 fld <- c k a i
153 case fld of
219 case fld of
220+ EmptyField -> wrongType "boolField"
154 StringField str -> return $ StringField (f str)
221 StringField str -> return $ StringField (f str)
155− ListField _ _ -> fail $
222+ _ -> wrongType "ListField"
156− "Hakyll.Web.Template.Context.mapContext: " ++
224+ wrongType typ = fail $ "Hakyll.Web.Template.Context.mapContext: " ++
157− "can't map over a ListField!"
225+ "can't map over a " ++ typ ++ "!"
159--------------------------------------------------------------------------------
227--------------------------------------------------------------------------------
160-- | A context that allows snippet inclusion. In processed file, use as:
228-- | A context that allows snippet inclusion. In processed file, use as:
@@ -163,15 +231,15 @@ mapContext f (Context c) = Context $ \k a i -> do
163-- > $snippet("path/to/snippet/")$
231-- > $snippet("path/to/snippet/")$
166−-- The contents of the included file will not be interpolated.
234+-- The contents of the included file will not be interpolated like @partial@
168snippetField :: Context String
237snippetField :: Context String
169snippetField = functionField "snippet" f
238snippetField = functionField "snippet" f
171 f [contentsPath] _ = loadBody (fromFilePath contentsPath)
240 f [contentsPath] _ = loadBody (fromFilePath contentsPath)
172− f _ i = error $
241+ f [] _ = fail "No argument to function 'snippet()'"
173− "Too many arguments to function 'snippet()' in item " ++
242+ f _ _ = fail "Too many arguments to function 'snippet()'"
174− show (itemIdentifier i)
176--------------------------------------------------------------------------------
244--------------------------------------------------------------------------------
177-- | A context that contains (in that order)
245-- | A context that contains (in that order)
@@ -191,8 +259,7 @@ defaultContext =
191 metadataField `mappend`
259 metadataField `mappend`
192 urlField "url" `mappend`
260 urlField "url" `mappend`
193 pathField "path" `mappend`
261 pathField "path" `mappend`
194− titleField "title" `mappend`
262+ titleField "title"
198--------------------------------------------------------------------------------
265--------------------------------------------------------------------------------
@@ -210,15 +277,20 @@ bodyField key = field key $ return . itemBody
210-- | Map any field to its metadata value, if present
277-- | Map any field to its metadata value, if present
211metadataField :: Context a
278metadataField :: Context a
212metadataField = Context $ \k _ i -> do
279metadataField = Context $ \k _ i -> do
213− 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
214− maybe empty (return . StringField) value
284+ maybe empty' (return . StringField) value
217--------------------------------------------------------------------------------
287--------------------------------------------------------------------------------
218-- | Absolute url to the resulting item
288-- | Absolute url to the resulting item
219urlField :: String -> Context a
289urlField :: String -> Context a
220−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
221− fmap (maybe empty toUrl) . getRoute . itemIdentifier
293+ fmap (maybe empty' toUrl) $ getRoute id
224--------------------------------------------------------------------------------
296--------------------------------------------------------------------------------
@@ -269,6 +341,12 @@ titleField = mapContext takeBaseName . pathField
269-- that begins with @yyyy-mm-dd@ . For example:
341-- that begins with @yyyy-mm-dd@ . For example:
270-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
342-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
271-- 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.
273dateField :: String -- ^ Key in which the rendered date should be placed
351dateField :: String -- ^ Key in which the rendered date should be placed
274 -> String -- ^ Format to use on the date
352 -> String -- ^ Format to use on the date
@@ -279,7 +357,7 @@ dateField = dateFieldWith defaultTimeLocale
279--------------------------------------------------------------------------------
357--------------------------------------------------------------------------------
280-- | This is an extended version of 'dateField' that allows you to
358-- | This is an extended version of 'dateField' that allows you to
281-- 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
282−-- details, see 'dateField'.
360+-- details, see 'dateField' and 'formatTime'.
283dateFieldWith :: TimeLocale -- ^ Output time locale
361dateFieldWith :: TimeLocale -- ^ Output time locale
284 -> String -- ^ Destination key
362 -> String -- ^ Destination key
285 -> String -- ^ Format to use on the date
363 -> String -- ^ Format to use on the date
@@ -305,7 +383,8 @@ getItemUTC locale id' = do
305 maybe empty' return $ msum $
383 maybe empty' return $ msum $
306 [tryField "published" fmt | fmt <- formats] ++
384 [tryField "published" fmt | fmt <- formats] ++
307 [tryField "date" fmt | fmt <- formats] ++
385 [tryField "date" fmt | fmt <- formats] ++
308− [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]
310 empty' = fail $ "Hakyll.Web.Template.Context.getItemUTC: " ++
389 empty' = fail $ "Hakyll.Web.Template.Context.getItemUTC: " ++
311 "could not parse time for " ++ show id'
390 "could not parse time for " ++ show id'
@@ -333,6 +412,7 @@ getItemModificationTime identifier = do
335--------------------------------------------------------------------------------
414--------------------------------------------------------------------------------
415+-- | Creates a field with the last modification date of the underlying item.
336modificationTimeField :: String -- ^ Key
416modificationTimeField :: String -- ^ Key
337 -> String -- ^ Format
417 -> String -- ^ Format
338 -> Context a -- ^ Resulting context
418 -> Context a -- ^ Resulting context
@@ -340,6 +420,8 @@ modificationTimeField = modificationTimeFieldWith defaultTimeLocale
342--------------------------------------------------------------------------------
422--------------------------------------------------------------------------------
423+-- | Creates a field with the last modification date of the underlying item
424+-- in a custom localisation format (see 'formatTime').
343modificationTimeFieldWith :: TimeLocale -- ^ Time output locale
425modificationTimeFieldWith :: TimeLocale -- ^ Time output locale
344 -> String -- ^ Key
426 -> String -- ^ Key
345 -> String -- ^ Format
427 -> String -- ^ Format
@@ -378,10 +460,11 @@ teaserFieldWithSeparator separator key snapshot = field key $ \item -> do
380--------------------------------------------------------------------------------
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.
381missingField :: Context a
465missingField :: Context a
382−missingField = Context $ \k _ i -> fail $
466+missingField = Context $ \k _ _ -> noResult $
383− "Missing field $" ++ k ++ "$ in context for item " ++
467+ "Missing field '" ++ k ++ "' in context"
384− show (itemIdentifier i)
386parseTimeM :: Bool -> TimeLocale -> String -> String -> Maybe UTCTime
469parseTimeM :: Bool -> TimeLocale -> String -> String -> Maybe UTCTime
387#if MIN_VERSION_time(1,5,0)
470#if MIN_VERSION_time(1,5,0)
@@ -389,3 +472,10 @@ parseTimeM = TF.parseTimeM
390parseTimeM _ = 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