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1. class FromForm a

   http-api-data	Web.FormUrlEncoded

   Parse Form into a value. An example type and instance:

   data Person = Person
   { name :: String
   , age  :: Int }
   
   instance FromForm Person where
   fromForm f = Person
   <$> parseUnique "name" f
   <*> parseUnique "age"  f
   

   Instead of manually writing FromForm instances you can use a default generic implementation of fromForm. To do that, simply add deriving Generic clause to your datatype and declare a FromForm instance for your datatype without giving definition for fromForm. For instance, the previous example can be simplified into this:

   data Person = Person
   { name :: String
   , age  :: Int
   } deriving (Generic)
   
   instance FromForm Person
   

   The default implementation of fromForm is genericFromForm. It only works for records and it will use parseQueryParam for each field's value.

2. class FromFormKey k

   http-api-data	Web.FormUrlEncoded

   Typeclass for types that can be parsed from keys of a Form. This is the reverse of ToFormKey.

3. class ToForm a

   http-api-data	Web.FormUrlEncoded

   Convert a value into Form. An example type and instance:

   {-# LANGUAGE OverloadedLists #-}
   
   data Person = Person
   { name :: String
   , age  :: Int }
   
   instance ToForm Person where
   toForm person =
   [ ("name", toQueryParam (name person))
   , ("age", toQueryParam (age person)) ]
   

   Instead of manually writing ToForm instances you can use a default generic implementation of toForm. To do that, simply add deriving Generic clause to your datatype and declare a ToForm instance for your datatype without giving definition for toForm. For instance, the previous example can be simplified into this:

   data Person = Person
   { name :: String
   , age  :: Int
   } deriving (Generic)
   
   instance ToForm Person
   

   The default implementation of toForm is genericToForm.

4. class ToFormKey k

   http-api-data	Web.FormUrlEncoded

   Typeclass for types that can be used as keys in a Form-like container (like Map).

5. defaultFormOptions :: FormOptions

   http-api-data	Web.FormUrlEncoded

   Default encoding FormOptions.

   FormOptions
   { fieldLabelModifier = id
   }
   

6. fromForm :: FromForm a => Form -> Either Text a

   http-api-data	Web.FormUrlEncoded

   Parse Form into a value.

7. genericFromForm :: (Generic a, GFromForm a (Rep a)) => FormOptions -> Form -> Either Text a

   http-api-data	Web.FormUrlEncoded

   A Generic-based implementation of fromForm. This is used as a default implementation in FromForm. Note that this only works for records (i.e. product data types with named fields):

   data Person = Person
   { name :: String
   , age  :: Int
   } deriving (Generic)
   

   In this implementation each field's value gets decoded using parseQueryParam. Two field types are exceptions:
   • for values of type Maybe a an entry is parsed if present in the Form and the is decoded with parseQueryParam; if no entry is present result is Nothing;
   • for values of type [a] (except [Char]) all entries are parsed to produce a list of parsed values;
   Here's an example:

   data Post = Post
   { title    :: String
   , subtitle :: Maybe String
   , comments :: [String]
   } deriving (Generic, Show)
   
   instance FromForm Post
   

   >>> urlDecodeAsForm "comments=Nice%20post%21&comments=%2B1&title=Test" :: Either Text Post
   Right (Post {title = "Test", subtitle = Nothing, comments = ["Nice post!","+1"]})
   

8. genericToForm :: (Generic a, GToForm a (Rep a)) => FormOptions -> a -> Form

   http-api-data	Web.FormUrlEncoded

   A Generic-based implementation of toForm. This is used as a default implementation in ToForm. Note that this only works for records (i.e. product data types with named fields):

   data Person = Person
   { name :: String
   , age  :: Int
   } deriving (Generic)
   

   In this implementation each field's value gets encoded using toQueryParam. Two field types are exceptions:
   • for values of type Maybe a an entry is added to the Form only when it is Just x and the encoded value is toQueryParam x; Nothing values are omitted from the Form;
   • for values of type [a] (except [Char]) an entry is added for every item in the list; if the list is empty no entries are added to the Form;
   Here's an example:

   data Post = Post
   { title    :: String
   , subtitle :: Maybe String
   , comments :: [String]
   } deriving (Generic, Show)
   
   instance ToForm Post
   

   >>> urlEncodeAsFormStable Post { title = "Test", subtitle = Nothing, comments = ["Nice post!", "+1"] }
   "comments=Nice%20post%21&comments=%2B1&title=Test"
   

9. parseFormKey :: FromFormKey k => Text -> Either Text k

   http-api-data	Web.FormUrlEncoded

   Parse a key of a Form.

10. toForm :: ToForm a => a -> Form

    http-api-data	Web.FormUrlEncoded

    Convert a value into Form.

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