This module contains the core definitions for the Heist template system.
The Heist template system is based on XML/xhtml. It allows you to build custom XML-based markup languages. With Heist you can define your own domain-specific XML tags implemented with Haskell and use them in your templates.
The most important concept in Heist is the Splice
. Splices can be thought
of as functions that transform a node into a list of nodes. Heist then
substitutes the resulting list of nodes into your template in place of the
input node. Splice
is implemented as a type synonym type Splice m =
TemplateMonad m [Node]
, and TemplateMonad
has a function getParamNode
that lets you get the input node.
Suppose you have a place on your page where you want to display a link with
the text "Logout username" if the user is currently logged in or a link to
the login page if no user is logged in. Assume you have a function
getUser :: MyAppMonad (Maybe ByteString)
that gets the current user.
You can implement this functionality with a Splice
as follows:
import Data.ByteString.Char8 (ByteString) import qualified Data.ByteString.Char8 as B import qualified Text.XML.Expat.Tree as X import Text.Templating.Heist link :: ByteString -> ByteString -> Node link target text = X.Element "a" [("href", target)] [X.Text text] loginLink :: Node loginLink = link "/login" "Login" logoutLink :: ByteString -> Node logoutLink user = link "/logout" (B.append "Logout " user) loginLogoutSplice :: Splice MyAppMonad loginLogoutSplice = do user <- lift getUser return $ [maybe loginLink logoutLink user]
Next, you need to bind that splice to an XML tag. Heist stores information
about splices and templates in the TemplateState
data structure. The
following code demonstrates how this splice would be used.
mySplices = [ ("loginLogout", loginLogoutSplice) ] main = do ets <- loadTemplates "templates" $ foldr (uncurry bindSplice) emptyTemplateState mySplices let ts = either error id ets t <- runMyAppMonad $ renderTemplate ts "index" print $ maybe "Page not found" id t
Here we build up our TemplateState
by starting with emptyTemplateState and
applying bindSplice for all the splices we want to add. Then we pass this
to loadTemplates our final TemplateState
wrapped in an Either to handle
errors. Then we use this TemplateState
to render our templates.
- type Node = Node ByteString ByteString
- type Template = [Node]
- type Splice m = TemplateMonad m Template
- data TemplateMonad m a
- data TemplateState m
- addTemplate :: Monad m => ByteString -> Template -> TemplateState m -> TemplateState m
- emptyTemplateState :: MonadIO m => TemplateState m
- bindSplice :: Monad m => ByteString -> Splice m -> TemplateState m -> TemplateState m
- bindSplices :: Monad m => [(ByteString, Splice m)] -> TemplateState m -> TemplateState m
- lookupSplice :: Monad m => ByteString -> TemplateState m -> Maybe (Splice m)
- setTemplates :: Monad m => TemplateMap -> TemplateState m -> TemplateState m
- loadTemplates :: Monad m => FilePath -> TemplateState m -> IO (Either String (TemplateState m))
- hasTemplate :: Monad m => ByteString -> TemplateState m -> Bool
- addOnLoadHook :: Monad m => (Template -> IO Template) -> TemplateState m -> TemplateState m
- addPreRunHook :: Monad m => (Template -> m Template) -> TemplateState m -> TemplateState m
- addPostRunHook :: Monad m => (Template -> m Template) -> TemplateState m -> TemplateState m
- stopRecursion :: Monad m => TemplateMonad m ()
- getParamNode :: Monad m => TemplateMonad m Node
- runNodeList :: Monad m => [Node] -> Splice m
- getContext :: Monad m => TemplateMonad m TPath
- localParamNode :: Monad m => (Node -> Node) -> TemplateMonad m a -> TemplateMonad m a
- getsTS :: Monad m => (TemplateState m -> r) -> TemplateMonad m r
- getTS :: Monad m => TemplateMonad m (TemplateState m)
- putTS :: Monad m => TemplateState m -> TemplateMonad m ()
- modifyTS :: Monad m => (TemplateState m -> TemplateState m) -> TemplateMonad m ()
- restoreTS :: Monad m => TemplateState m -> TemplateMonad m ()
- evalTemplate :: Monad m => ByteString -> TemplateMonad m (Maybe Template)
- callTemplate :: Monad m => ByteString -> [(ByteString, ByteString)] -> TemplateMonad m (Maybe Template)
- renderTemplate :: Monad m => TemplateState m -> ByteString -> m (Maybe ByteString)
- renderWithArgs :: Monad m => [(ByteString, ByteString)] -> TemplateState m -> ByteString -> m (Maybe ByteString)
- bindStrings :: Monad m => [(ByteString, ByteString)] -> TemplateState m -> TemplateState m
- bindString :: Monad m => ByteString -> ByteString -> TemplateState m -> TemplateState m
- getDoc :: String -> IO (Either String InternalTemplate)
- parseDoc :: ByteString -> IO (Either String (Maybe ByteString, [Node]))
- bindStaticTag :: MonadIO m => TemplateState m -> IO (TemplateState m, StaticTagState)
Types
type Node = Node ByteString ByteStringSource
Heist templates are XML documents. The hexpat library is polymorphic over
the type of strings, so here we define a Node
alias to fix the string
types of the tag names and tag bodies to ByteString
.
A Template
is a forest of XML nodes. Here we deviate from the single
root node constraint of well-formed XML because we want to allow templates
to contain fragments of a document that may not have a single root.
type Splice m = TemplateMonad m TemplateSource
A Splice is a TemplateMonad computation that returns a Template
.
data TemplateMonad m a Source
TemplateMonad is the monad used for Splice
processing. TemplateMonad
provides "passthrough" instances for many of the monads you might use in
the inner monad.
MonadTrans TemplateMonad | MonadTrans instance |
MonadError e m => MonadError e (TemplateMonad m) | MonadError passthrough instance |
MonadReader r m => MonadReader r (TemplateMonad m) | MonadReader passthrough instance |
MonadState s m => MonadState s (TemplateMonad m) | MonadState passthrough instance |
Monad m => Monad (TemplateMonad m) | Monad instance |
Functor m => Functor (TemplateMonad m) | Functor instance |
Typeable1 m => Typeable1 (TemplateMonad m) | |
MonadFix m => MonadFix (TemplateMonad m) | MonadFix passthrough instance |
MonadPlus m => MonadPlus (TemplateMonad m) | MonadPlus passthrough instance |
(Monad m, Functor m) => Applicative (TemplateMonad m) | Applicative instance |
(Functor m, MonadPlus m) => Alternative (TemplateMonad m) | Alternative passthrough instance |
MonadIO m => MonadIO (TemplateMonad m) | MonadIO instance |
MonadCont m => MonadCont (TemplateMonad m) | MonadCont passthrough instance |
data TemplateState m Source
Holds all the state information needed for template processing. You will
build a TemplateState
using any of Heist's TemplateState m ->
TemplateState m
"filter" functions. Then you use the resulting
TemplateState
in calls to renderTemplate
.
Eq (TemplateState m) | |
Typeable1 m => Typeable (TemplateState m) | |
Monad m => Monoid (TemplateState m) |
Functions and declarations on TemplateState values
addTemplate :: Monad m => ByteString -> Template -> TemplateState m -> TemplateState mSource
Adds a template to the template state.
emptyTemplateState :: MonadIO m => TemplateState mSource
An empty template state, with Heist's default splices (<apply>
,
<bind>
, <ignore>
, and <markdown>
) mapped. The static tag is
not mapped here because it must be mapped manually in your application.
:: Monad m | |
=> ByteString | tag name |
-> Splice m | splice action |
-> TemplateState m | source state |
-> TemplateState m |
Binds a new splice declaration to a tag name within a TemplateState
.
:: Monad m | |
=> [(ByteString, Splice m)] | splices to bind |
-> TemplateState m | start state |
-> TemplateState m |
Binds a set of new splice declarations within a TemplateState
.
lookupSplice :: Monad m => ByteString -> TemplateState m -> Maybe (Splice m)Source
Convenience function for looking up a splice.
setTemplates :: Monad m => TemplateMap -> TemplateState m -> TemplateState mSource
Sets the templateMap in a TemplateState.
loadTemplates :: Monad m => FilePath -> TemplateState m -> IO (Either String (TemplateState m))Source
Traverses the specified directory structure and builds a TemplateState by loading all the files with a .tpl extension.
hasTemplate :: Monad m => ByteString -> TemplateState m -> BoolSource
Returns True
if the given template can be found in the template state.
Hook functions
Heist hooks allow you to modify templates when they are loaded and before and after they are run. Every time you call one of the addAbcHook functions the hook is added to onto the processing pipeline. The hooks processes the template in the order that they were added to the TemplateState.
The pre-run and post-run hooks are run before and after every template is run/rendered. You should be careful what code you put in these hooks because it can significantly affect the performance of your site.
addOnLoadHook :: Monad m => (Template -> IO Template) -> TemplateState m -> TemplateState mSource
Adds an on-load hook to a TemplateState
.
addPreRunHook :: Monad m => (Template -> m Template) -> TemplateState m -> TemplateState mSource
Adds a pre-run hook to a TemplateState
.
addPostRunHook :: Monad m => (Template -> m Template) -> TemplateState m -> TemplateState mSource
Adds a post-run hook to a TemplateState
.
TemplateMonad functions
stopRecursion :: Monad m => TemplateMonad m ()Source
Stops the recursive processing of splices. Consider the following example:
<foo> <bar> ... </bar> </foo>
Assume that "foo"
is bound to a splice procedure. Running the foo
splice will result in a list of nodes L
. Normally foo
will recursively
scan L
for splices and run them. If foo
calls stopRecursion
, L
will be included in the output verbatim without running any splices.
getParamNode :: Monad m => TemplateMonad m NodeSource
Gets the node currently being processed.
<speech author="Shakespeare"> To sleep, perchance to dream. </speech>
When you call getParamNode
inside the code for the speech
splice, it
returns the Node for the speech
tag and its children. getParamNode >>=
getChildren
returns a list containing one Text
node containing part of
Hamlet's speech. getParamNode >>= getAttribute "author"
would return
Just Shakespeare
.
runNodeList :: Monad m => [Node] -> Splice mSource
Performs splice processing on a list of nodes.
getContext :: Monad m => TemplateMonad m TPathSource
Gets the current context
localParamNode :: Monad m => (Node -> Node) -> TemplateMonad m a -> TemplateMonad m aSource
TemplateMonad's local
.
getsTS :: Monad m => (TemplateState m -> r) -> TemplateMonad m rSource
TemplateMonad's gets
.
getTS :: Monad m => TemplateMonad m (TemplateState m)Source
TemplateMonad's get
.
putTS :: Monad m => TemplateState m -> TemplateMonad m ()Source
TemplateMonad's put
.
modifyTS :: Monad m => (TemplateState m -> TemplateState m) -> TemplateMonad m ()Source
TemplateMonad's modify
.
restoreTS :: Monad m => TemplateState m -> TemplateMonad m ()Source
Restores the components of TemplateState that can get modified in
template calls. You should use this function instead of putTS
to restore
an old state. Thas was needed because doctypes needs to be in a global
scope as opposed to the template call local scope of state items such
as recursionDepth, curContext, and spliceMap.
Functions for running splices and templates
evalTemplate :: Monad m => ByteString -> TemplateMonad m (Maybe Template)Source
Looks up a template name evaluates it by calling runNodeList.
:: Monad m | |
=> ByteString | The name of the template |
-> [(ByteString, ByteString)] | Association list of (name,value) parameter pairs |
-> TemplateMonad m (Maybe Template) |
Renders a template with the specified parameters. This is the function to use when you want to call a template and pass in parameters from inside a splice.
renderTemplate :: Monad m => TemplateState m -> ByteString -> m (Maybe ByteString)Source
Renders a template from the specified TemplateState.
renderWithArgs :: Monad m => [(ByteString, ByteString)] -> TemplateState m -> ByteString -> m (Maybe ByteString)Source
Renders a template with the specified arguments passed to it. This is a convenience function for the common pattern of calling renderTemplate after using bindString, bindStrings, or bindSplice to set up the arguments to the template.
bindStrings :: Monad m => [(ByteString, ByteString)] -> TemplateState m -> TemplateState mSource
Binds a list of constant string splices.
bindString :: Monad m => ByteString -> ByteString -> TemplateState m -> TemplateState mSource
Binds a single constant string splice.
Misc functions
parseDoc :: ByteString -> IO (Either String (Maybe ByteString, [Node]))Source
Turns an in-memory XML/XHTML bytestring into a (doctype,'[Node]') pair.
bindStaticTag :: MonadIO m => TemplateState m -> IO (TemplateState m, StaticTagState)Source
Modifies a TemplateState to include a "static" tag. The static tag is
not bound automatically with the other default Heist tags. This is because
this function also returns StaticTagState, so the user will be able to
clear it with the clearStaticTagCache
function.