Difference between revisions of "Web/Libraries/Formlets"
SimonHengel (talk | contribs) (added more detailed instructions) |
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== A working example == |
== A working example == |
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+ | Below is a self-contained example that uses |
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+ | [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/formlets Formlets] |
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+ | and |
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+ | [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Server HAppS-Server]. |
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+ | |||
+ | === Prepare your system === |
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+ | First install Formlets and HAppS-Server on your system: |
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+ | |||
+ | <pre> |
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+ | $ cabal install formlets happs-server |
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+ | </pre> |
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+ | |||
+ | === The example code === |
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+ | Put the following in a file called <hask>Main.hs</hask>: |
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− | This example code has shown to work with the latest formlets release (0.4.7 at the moment of this writing): |
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<haskell> |
<haskell> |
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module Main where |
module Main where |
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main = simpleHTTP (nullConf {port = 5000}) (handleDate ++ handleUser) |
main = simpleHTTP (nullConf {port = 5000}) (handleDate ++ handleUser) |
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</haskell> |
</haskell> |
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+ | |||
+ | === Running the example === |
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+ | Start up the HAppS server with |
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+ | <pre> |
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+ | $ runhaskell Main.hs |
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+ | </pre> |
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+ | and point your web browser at http://localhost:5000/date/ |
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+ | and http://localhost:5000/user/. |
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== How it works == |
== How it works == |
Revision as of 20:27, 9 April 2009
Introduction
Formlets are a way of building HTML forms that are type-safe, handle errors, abstract and are easy to combine into bigger forms. Here's an example:
name :: Form String
name = input Nothing
The input function takes a Maybe String, and produces a XHtmlForm String. The Maybe String is used for default values. If you give it a nothing, it won't have a default value. If you pass in a (Just "value"), it will be pre-populated with the value "value".
You can easily combine formlets using the Applicative Functor combinators. Suppose you have a User-datatype:
data User = User {name :: String, age :: Integer, email :: String}
You can then build a form that produces a user:
userForm :: Form User
userForm = User <$> name <*> inputInteger <*> input Nothing
You can also have more advanced widgets, like a radio-choice, that's where you use enumRadio:
enumRadio :: (Monad m, Enum a) => [(a, String)] -> Maybe a -> Form a
So it asks for a list of pairs with a value and the corresponding label, a possible default-value and it will return something of type a.
chooseBool :: Form Bool
chooseBool = enumRadio [(True, "Yes"), (False, "No")] True
Now we have a widget for booleans that we can use everywhere in our forms!
The basics
Simple validation
Monadic validation
A working example
Below is a self-contained example that uses Formlets and HAppS-Server.
Prepare your system
First install Formlets and HAppS-Server on your system:
$ cabal install formlets happs-server
The example code
Put the following in a file called Main.hs
:
module Main where
import HAppS.Server
import Control.Applicative
import Control.Applicative.Error
import Control.Applicative.State
import Text.XHtml.Strict.Formlets
import Text.XHtml.Strict ((+++), (<<), (!))
import qualified Text.XHtml.Strict as X
import qualified Data.Map as M
type MyForm a = XHtmlForm IO a
data Date = Date {month :: Integer, day :: Integer} deriving Show
validDate :: Date -> Bool
validDate (Date m d) = m `elem` [1..12] && d `elem` [1..31]
dateComponent :: MyForm Date
dateComponent = Date <$> inputInteger (Just 1) <*> inputInteger (Just 16)
dateFull :: MyForm Date
dateFull = dateComponent `check` ensure validDate "This is not a valid date"
handleDate :: [ServerPart Response]
handleDate = withForm "date" dateFull showErrorsInline (\d -> okHtml $ show d)
data User = User {name :: String, pass :: String, birthdate :: Date} deriving Show
userFull :: MyForm User
userFull = User <$> input Nothing <*> password Nothing <*> dateFull
handleUser = withForm "user" userFull showErrorsInline (\u -> okHtml $ show u)
withForm :: String -> MyForm a -> (X.Html -> [String] -> Web Response) -> (a -> Web Response) -> [ServerPart Response]
withForm name frm handleErrors handleOk =
[dir name
[ method GET $ createForm [] frm >>= okHtml
, withDataFn lookPairs $ \d -> [method POST $ handleOk' $ simple d]
]
]
where handleOk' d = do let (extractor, html, _) = runFormState d "" frm
v <- liftIO extractor
case v of
Failure faults -> do f <- createForm d frm
handleErrors f faults
Success s -> handleOk s
simple d = map (\(k,v) -> (k, Left v)) d
showErrorsInline :: X.Html -> [String] -> Web Response
showErrorsInline renderedForm errors =
okHtml $ X.toHtml (show errors) +++ renderedForm
createForm :: Env -> MyForm a -> Web X.Html
createForm env frm = do
let (extractor, xml, endState) = runFormState env "" frm
xml' <- liftIO xml
return $ X.form ! [X.method "POST"] << (xml' +++ X.submit "submit" "Submit")
okHtml :: (X.HTML a) => a -> Web Response
okHtml content = ok $ toResponse $ htmlPage $ content
htmlPage :: (X.HTML a) => a -> X.Html
htmlPage content = (X.header << (X.thetitle << "Testing forms")) +++ (X.body << content)
main = simpleHTTP (nullConf {port = 5000}) (handleDate ++ handleUser)
Running the example
Start up the HAppS server with
$ runhaskell Main.hs
and point your web browser at http://localhost:5000/date/ and http://localhost:5000/user/.