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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 :: XHtmlForm 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 combinators from Applicative. 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

The basics

How it works

Advanced: rolling your own output type