Hakyll.Web.Template.Context

This module provides Contexts which are used to expand expressions in templates and allow for arbitrary customisation.

Templates define a small expression DSL which consists of strings, identifiers and function application. There is no type system, every value is a string and on the top level they get substituted verbatim into the page.

For example, you can build a context that contains

… <> functionField "concat" (const . concat) <> …

which will allow you to use the concat identifier as a function that takes arbitrarily many strings and concatenates them to a new string:

$partial(concat("templates/categories/", category))$

This will evaluate the category field in the context, then prepend the path, and include the referenced file as a template.

Documentation

data ContextField

Mostly for internal usage

Constructors

EmptyField

StringField String

forall a. ListField (Context a) [Item a]

newtype Context a

The Context monoid. Please note that the order in which you compose the items is important. For example in

field "A" f1 <> field "A" f2

the first context will overwrite the second. This is especially important when something is being composed with metadataField (or defaultContext). If you want your context to be overwritten by the metadata fields, compose it from the right:

metadataField <> field "date" fDate

Constructors

Context

Fields

• unContext :: String -> [String] -> Item a -> Compiler ContextField

Instances

Semigroup (Context a)

Tries to find a key in the left context, or when that fails in the right context.

Defined in Hakyll.Web.Template.Context

Methods

(<>) :: Context a -> Context a -> Context a

sconcat :: NonEmpty (Context a) -> Context a

stimes :: Integral b => b -> Context a -> Context a

Monoid (Context a)

Defined in Hakyll.Web.Template.Context

Methods

mempty :: Context a

mappend :: Context a -> Context a -> Context a

mconcat :: [Context a] -> Context a

field

Arguments

:: String

Key

-> (Item a -> Compiler String)

Function that constructs a value based on the item (e.g. accessing metadata)

-> Context a

Constructs a new field for a Context. If the key matches, the compiler is run and its result is substituted in the template.

If the compiler fails, the field will be considered non-existent in an $if()$ macro or ultimately break the template application (unless the key is found in another context when using <>). Use empty or noResult for intentional failures of fields used in $if()$, to distinguish them from exceptions thrown with fail.

boolField :: String -> (Item a -> Bool) -> Context a

Creates a field to use with the $if()$ template macro. Attempting to substitute the field into the template will cause an error.

constField

Arguments

:: String

Key

-> String

Value

-> Context a

Creates a field that does not depend on the Item but always yields the same string

listField :: String -> Context a -> Compiler [Item a] -> Context b

Creates a list field to be consumed by a $for(…)$ expression. The compiler returns multiple items which are rendered in the loop body with the supplied context.

listFieldWith :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b

Creates a list field like listField, but supplies the current page to the compiler.

functionField

Arguments

:: String

Key

-> ([String] -> Item a -> Compiler String)

Function

-> Context a

Creates a variadic function field.

The function will be called with the dynamically evaluated string arguments from the template as well as the page that is currently rendered.

mapContext :: (String -> String) -> Context a -> Context a

Transform the respective string results of all fields in a context. For example,

mapContext (++"c") (constField "x" "a" <> constField "y" "b")

is equivalent to

constField "x" "ac" <> constField "y" "bc"

defaultContext :: Context String

A context that contains (in that order)

1. A $body$ field
2. Metadata fields
3. A $url$ urlField
4. A $path$ pathField
5. A $title$ titleField

bodyField :: String -> Context String

Constructs a field that contains the body of the item.

metadataField :: Context a

Map any field to its metadata value, if present

urlField :: String -> Context a

Absolute url to the resulting item

pathField :: String -> Context a

Filepath of the underlying file of the item

titleField :: String -> Context a

This title field takes the basename of the underlying file by default

snippetField :: Context String

A context that allows snippet inclusion. In processed file, use as:

...
$snippet("path/to/snippet/")$
...

The contents of the included file will not be interpolated like partial does it.

dateField

Arguments

:: String

Key in which the rendered date should be placed

-> String

Format to use on the date

-> Context a

Resulting context

When the metadata has a field called published in one of the following formats then this function can render the date.

• Mon, 06 Sep 2010 00:01:00 +0000

• Mon, 06 Sep 2010 00:01:00 UTC

• Mon, 06 Sep 2010 00:01:00

• 2010-09-06T00:01:00+0000

• 2010-09-06T00:01:00Z

• 2010-09-06T00:01:00

• 2010-09-06 00:01:00+0000

• 2010-09-06 00:01:00

• September 06, 2010 00:01 AM

Following date-only formats are supported too (00:00:00 for time is assumed)

• 2010-09-06

• September 06, 2010

Alternatively, when the metadata has a field called path in a folder/yyyy-mm-dd-title.extension format (the convention for pages) and no published metadata field set, this function can render the date. This pattern matches the file name or directory names that begins with yyyy-mm-dd . For example: folder/yyyy-mm-dd-titledist/main.extension . In case of multiple matches, the rightmost one is used.

As another alternative, if none of the above matches, and the file has a path which contains nested directories specifying a date, then that date will be used. In other words, if the path is of the form **/yyyymmdd/main.extension . As above, in case of multiple matches, the rightmost one is used.

dateFieldWith

Arguments

:: TimeLocale

Output time locale

-> String

Destination key

-> String

Format to use on the date

-> Context a

Resulting context

This is an extended version of dateField that allows you to specify a time locale that is used for outputting the date. For more details, see dateField and formatTime.

getItemUTC

Arguments

:: (MonadMetadata m, MonadFail m)

=> TimeLocale

Output time locale

-> Identifier

Input page

-> m UTCTime

Parsed UTCTime

Parser to try to extract and parse the time from the published field or from the filename. See dateField for more information. Exported for user convenience.

getItemModificationTime :: Identifier -> Compiler UTCTime

Get the time on which the actual file was last modified. This only works if there actually is an underlying file, of couse.

modificationTimeField

Arguments

:: String

Key

-> String

Format

-> Context a

Resulting context

Creates a field with the last modification date of the underlying item.

modificationTimeFieldWith

Arguments

:: TimeLocale

Time output locale

-> String

Key

-> String

Format

-> Context a

Resulting context

Creates a field with the last modification date of the underlying item in a custom localisation format (see formatTime).

teaserField

Arguments

:: String

Key to use

-> Snapshot

Snapshot to load

-> Context String

Resulting context

A context with "teaser" key which contain a teaser of the item. The item is loaded from the given snapshot (which should be saved in the user code before any templates are applied).

teaserFieldWithSeparator

Arguments

:: String

Separator to use

-> String

Key to use

-> Snapshot

Snapshot to load

-> Context String

Resulting context

A context with "teaser" key which contain a teaser of the item, defined as the snapshot content before the teaser separator. The item is loaded from the given snapshot (which should be saved in the user code before any templates are applied).

missingField :: Context a

Constantly reports any field as missing. Mostly for internal usage, it is the last choice in every context used in a template application.