Safe Haskell | Safe-Infered |
---|
web-routes-boomerang
makes it easy to use write custom
pretty-printers and parsers for your URL types. Instead of writing a
parser and a separate pretty-printer you can specify both at once by
using the boomerang
library:
http://hackage.haskell.org/package/boomerang
This demo will show the basics of getting started.
First we need to enable some language extensions:
{-# LANGUAGE TemplateHaskell, TypeOperators, OverloadedStrings #-}
module Main where
Note in the imports that we hide (id, (.))
from the Prelude and
use the versions from Control.Category instead.
import Prelude hiding (id, (.)) import Control.Category (Category(id, (.))) import Control.Monad.Trans (MonadIO(liftIO)) import Text.Boomerang.TH (derivePrinterParsers) import Web.Routes (Site(..), RouteT(..), decodePathInfo, encodePathInfo, runSite, showURL) import Web.Routes.Boomerang (Router, (<>), (</>), int, parse1, boomerangSiteRouteT, anyString, parseStrings)
Next we define a data type that represents our sitemap.
-- | the routes data Sitemap = Home | UserOverview | UserDetail Int | Article Int String deriving (Eq, Show)
To use the Sitemap
type with boomerang
we need to call derivePrinterParsers
:
$(derivePrinterParsers ''Sitemap)
That will create new combinators corresponding to the constructors for
Sitemap
. They will be named, rHome
, rUserOverview
, etc.
Now we can specify how the Sitemap
type is mapped to a url and back:
sitemap :: Router Sitemap sitemap = ( rHome <> "users" . users <> rArticle . ("article" </> int . "-" . anyString) ) where users = rUserOverview <> rUserDetail </> int
The mapping looks like this:
/ <=> Home /users <=> UserOverview /users/<int> <=> UserDetail <int> /article/<int>-<string> <=> Article <int> <string>
Next we have our function which maps a parsed route to the handler for
that route. (There is nothing boomerang
specific about this
function):
handle :: Sitemap -> RouteT Sitemap IO () handle url = case url of _ -> do liftIO $ print url s <- showURL url liftIO $ putStrLn s
Normally the case
statement would match on the different constructors and map them to different handlers. But in this case we use the same handler for all constructors. Also, instead of running in the IO monad, we would typically use a web framework monad like Happstack's ServerPartT
.
The handler does two things:
- prints the parsed url
- unparses the url and prints it
We now have two pieces:
-
sitemap
- which converts urls to theSitemap
type and back -
handle
- which mapsSitemap
to handlers
We tie these two pieces together use boomerangSiteRouteT
:
site :: Site Sitemap (IO ()) site = boomerangSiteRouteT handle sitemap
This gives as a standard Site
value that we can use with runSite
or with framework specific wrappers like implSite
.
If we were not using RouteT
then we could use boomerangSite
instead.
Now we can create a simple test function that takes the path info part of a url and runs our site:
test :: ByteString -- ^ path info of incoming url -> IO () test path = case runSite "" site (decodePathInfo path) of (Left e) -> putStrLn e (Right io) -> io
We can use it like this:
ghci> test users/1 UserDetail 1 users/1
Here is a simple wrapper to call test interactively:
-- | interactively call 'test' main :: IO () main = mapM_ test =<< fmap lines getContents
Here are two more helper functions you can use to experiment interactively:
-- | a little function to test rendering a url showurl :: Sitemap -> String showurl url = let (ps, params) = formatPathSegments site url in (encodePathInfo ps params)
-- | a little function to test parsing a url testParse :: String -> Either String Sitemap testParse pathInfo = case parsePathSegments site $ decodePathInfo pathInfo of (Left e) -> Left (show e) (Right a) -> Right a
- module Text.Boomerang
- module Text.Boomerang.Texts
- type Router a b = PrinterParser TextsError [Text] a b
- boomerangSite :: ((url -> [(Text, Maybe Text)] -> Text) -> url -> a) -> Router () (url :- ()) -> Site url a
- boomerangSiteRouteT :: (url -> RouteT url m a) -> Router () (url :- ()) -> Site url (m a)
Documentation
module Text.Boomerang
module Text.Boomerang.Texts
type Router a b = PrinterParser TextsError [Text] a bSource
'Router a b' is a simple type alias for 'PrinterParser TextsError [Text] a b'