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" 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

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

-> HeistState (Handler b b)

Initial HeistState

-> SnapletInit b (Heist b)

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

addTemplates

Arguments

:: HasHeist 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

=> 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.

modifyHeistTS

Arguments

:: HasHeist b

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

HeistState modifying function

-> Initializer b v ()

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

withHeistTS

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, SnapletSplice b v)]

Splices to bind

-> 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

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 ()

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

heistServeSingle

Arguments

:: HasHeist b

=> ByteString

Template name

-> Handler b v ()

Analogous 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, SnapletSplice b v)]

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, SnapletSplice b v)]

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 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)] -> HeistState (Handler b b) -> HeistState (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.