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) }
 mkLabels [''App]

 instance HasHeist App where heistLens = subSnaplet heist

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

Methods

heistLens :: Lens (Snaplet b) (Snaplet (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 :: FilePath -> SnapletInit b (Heist b)

The Initializer for Heist.

addTemplates :: HasHeist b => ByteString -> Initializer b v ()

Adds templates to the Heist TemplateState. 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 :: HasHeist b => ByteString -> FilePath -> Initializer b v ()

Adds templates to the Heist TemplateState, and lets you specify where they are found in the filesystem.

modifyHeistTS :: HasHeist b => (TemplateState (Handler b b) -> TemplateState (Handler b b)) -> Initializer b v ()

More general function allowing arbitrary TemplateState modification. Without this function you wouldn't be able to bind more complicated splices like the cache tag.

withHeistTS :: HasHeist b => (TemplateState (Handler b b) -> a) -> Handler b v a

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

addSplices :: HasHeist b => [(Text, SnapletSplice b v)] -> Initializer b v ()

Allows snaplets to add splices.

Handler Functions

This section contains functions in the Handler monad that you'll use in processing requests.

render :: HasHeist b => ByteString -> Handler b v ()

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

renderAs :: HasHeist b => ByteString -> ByteString -> 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 ()

Analogous to fileServe. If the template specified in the request path is not found, it returns empty.

heistServeSingle :: HasHeist b => ByteString -> Handler b v ()

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

heistLocal :: HasHeist b => (TemplateState (Handler b b) -> TemplateState (Handler b b)) -> Handler b v a -> Handler b v a

Runs a handler with a modified TemplateState. 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 :: HasHeist b => [(Text, SnapletSplice b v)] -> Handler b v a -> Handler b v a

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

renderWithSplices :: HasHeist b => ByteString -> [(Text, SnapletSplice b v)] -> 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 TemplateState 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 SnapletSplice instead of Splice.

data SnapletHeist b v a

Monad for working with Heist's API from within a snaplet.

Instances

MonadSnaplet SnapletHeist

MonadSnaplet instance gives us access to the snaplet infrastructure.

MonadState v (SnapletHeist b v)

Monad (SnapletHeist b v)

Functor (SnapletHeist b v)

MonadPlus (SnapletHeist b v)

Applicative (SnapletHeist b v)

MonadCatchIO (SnapletHeist b v)

Alternative (SnapletHeist b v)

MonadIO (SnapletHeist b v)

MonadSnap (SnapletHeist b v)

MonadReader (Lens (Snaplet b) (Snaplet v)) (SnapletHeist b v)

type SnapletSplice b v = SnapletHeist b v Template

Type alias for convenience.

liftHeist :: HeistT (Handler b b) a -> SnapletHeist b v a

Lifts a HeistT action into SnapletHeist. Use this with all the functions from the Heist API.

liftHandler :: Handler b v a -> SnapletHeist b v a

Lifts a Handler into SnapletHeist.

liftAppHandler :: Handler b b a -> SnapletHeist b v a

Lifts a (Handler b b) into SnapletHeist.

liftWith :: Lens (Snaplet b) (Snaplet v') -> Handler b v' a -> SnapletHeist b v a

Common idiom for the combination of liftHandler and withTop.

bindSnapletSplices :: Lens (Snaplet b) (Snaplet v) -> [(Text, SnapletSplice b v)] -> TemplateState (Handler b b) -> TemplateState (Handler b b)

SnapletSplices version of bindSplices.

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.