Snap.Snaplet.Heist

The Heist snaplet makes it easy to add Heist to your application and use it in other snaplets.

Heist and its type class

data Heist b

The state for the Heist snaplet. To use the Heist snaplet in your app include this in your application state and use heistInit to initialize it. The type parameter b will typically be the base state type for your application.

class HasHeist b where

A single snaplet should never need more than one instance of Heist as a subsnaplet. This type class allows you to make it easy for other snaplets to get the lens that identifies the heist snaplet. Here's an example of how the heist snaplet might be declared:

 data App = App { _heist :: Snaplet (Heist App) }
 makeLenses ''App

 instance HasHeist App where heistLens = subSnaplet heist

 appInit = makeSnaplet "app" "" Nothing $ do
     h <- nestSnaplet "heist" heist $ heistInit "templates"
     addSplices myAppSplices
     return $ App h

Methods

heistLens :: SnapletLens (Snaplet b) (Heist b)

A lens to the Heist snaplet. The b parameter to Heist will typically be the base state of your application.

Initializer Functions

This section contains functions for use in setting up your Heist state during initialization.

heistInit

Arguments

:: FilePath

Path to templates

-> SnapletInit b (Heist b)

The Initializer for Heist. This function is a convenience wrapper around heistInit' that uses defaultHeistState and sets up routes for all the templates.

heistInit'

Arguments

:: FilePath

Path to templates

-> HeistConfig (Handler b b)

Initial HeistConfig

-> SnapletInit b (Heist b)

A lower level Initializer for Heist. This initializer requires you to specify the initial HeistConfig. It also does not add any routes for templates, allowing you complete control over which templates get routed.

addTemplates

Arguments

:: HasHeist b

=> Snaplet (Heist b)

-> ByteString

The url prefix for the template routes

-> Initializer b v ()

Adds templates to the Heist HeistState. Other snaplets should use this function to add their own templates. The templates are automatically read from the templates directory in the current snaplet's filesystem root.

addTemplatesAt

Arguments

:: HasHeist b

=> Snaplet (Heist b)

-> ByteString

URL prefix for template routes

-> FilePath

Path to templates

-> Initializer b v ()

Adds templates to the Heist HeistState, and lets you specify where they are found in the filesystem. Note that the path to the template directory is an absolute path. This allows you more flexibility in where your templates are located, but means that you have to explicitly call getSnapletFilePath if you want your snaplet to use templates within its normal directory structure.

addConfig :: Snaplet (Heist b) -> HeistConfig (Handler b b) -> Initializer b v ()

Adds more HeistConfig data using mappend with whatever is currently there. This is the preferred method for adding all four kinds of splices as well as new templates.

modifyHeistState

Arguments

:: HasHeist b

=> (HeistState (Handler b b) -> HeistState (Handler b b))

HeistState modifying function

-> Initializer b v ()

More general function allowing arbitrary HeistState modification.

withHeistState

Arguments

:: HasHeist b

=> (HeistState (Handler b b) -> a)

HeistState function to run

-> Handler b v a

Runs a function on with the Heist snaplet's HeistState.

addSplices

Arguments

:: HasHeist b

=> [(Text, SnapletISplice b)]

Splices to bind

-> Initializer b v ()

Allows snaplets to add interpreted splices.

NOTE: The splices added with this function will not work if you render your templates with cRender. To add splices that work with cRender, you have to use the addConfig function to add compiled splices or load time splices.

Handler Functions

This section contains functions in the Handler monad that you'll use in processing requests. Functions beginning with a c prefix use compiled template rendering. The other functions use the older interpreted rendering. Splices added with addSplices will only work if you use interpreted rendering.

cRender

Arguments

:: HasHeist b

=> ByteString

Template name

-> Handler b v ()

Renders a compiled template as text/html. If the given template is not found, this returns empty.

cRenderAs

Arguments

:: HasHeist b

=> ByteString

Content type to render with

-> ByteString

Template name

-> Handler b v ()

Renders a compiled template as the given content type. If the given template is not found, this returns empty.

cHeistServe :: HasHeist b => Handler b v ()

A compiled version of heistServe.

cHeistServeSingle

Arguments

:: HasHeist b

=> ByteString

Template name

-> Handler b v ()

Analogous to fileServeSingle. If the given template is not found, this throws an error.

render

Arguments

:: HasHeist b

=> ByteString

Template name

-> Handler b v ()

Renders a template as text/html. If the given template is not found, this returns empty.

renderAs

Arguments

:: HasHeist b

=> ByteString

Content type to render with

-> ByteString

Template name

-> Handler b v ()

Renders a template as the given content type. If the given template is not found, this returns empty.

heistServe :: HasHeist b => Handler b v ()

A handler that serves all the templates (similar to serveDirectory). If the template specified in the request path is not found, it returns empty. Also, this function does not serve any templates beginning with an underscore. This gives you a way to prevent some templates from being served. For example, you might have a template that contains only the navbar of your pages, and you probably wouldn't want that template to be visible to the user as a standalone template. So if you put it in a file called "_nav.tpl", this function won't serve it.

heistServeSingle

Arguments

:: HasHeist b

=> ByteString

Template name

-> Handler b v ()

Handler for serving a single template (similar to fileServeSingle). If the given template is not found, this throws an error.

heistLocal

Arguments

:: HasHeist b

=> (HeistState (Handler b b) -> HeistState (Handler b b))

HeistState modifying function

-> Handler b v a

Handler to run

-> Handler b v a

Runs a handler with a modified HeistState. You might want to use this if you had a set of splices which were customised for a specific action. To do that you would do:

 heistLocal (bindSplices mySplices) handlerThatNeedsSplices

withSplices

Arguments

:: HasHeist b

=> [(Text, SnapletISplice b)]

Splices to bind

-> Handler b v a

Handler to run

-> Handler b v a

Runs an action with additional splices bound into the Heist HeistState.

renderWithSplices

Arguments

:: HasHeist b

=> ByteString

Template name

-> [(Text, SnapletISplice b)]

Splices to bind

-> Handler b v ()

Renders a template with a given set of splices. This is syntax sugar for a common combination of heistLocal, bindSplices, and render.

Writing Splices

As can be seen in the type signature of heistLocal, the internal HeistState used by the heist snaplet is parameterized by (Handler b b). The reasons for this are beyond the scope of this discussion, but the result is that lift inside a splice only works with Handler b b actions. When you're writing your own snaplets you obviously would rather work with Handler b v so your local snaplet's state is available. We provide the SnapletHeist monad to make this possible. The general rule is that when you're using Snaplets and Heist, use SnapletHeist instead of HeistT (previously called TemplateMonad) and use SnapletISplice instead of Splice.

type SnapletHeist b m a = HeistT (Handler b b) m a

type SnapletCSplice b = SnapletHeist b IO (DList (Chunk (Handler b b)))

type SnapletISplice b = SnapletHeist b (Handler b b) Template

clearHeistCache :: Heist b -> IO ()

Clears data stored by the cache tag. The cache tag automatically reloads its data when the specified TTL expires, but sometimes you may want to trigger a manual reload. This function lets you do that.