Safe Haskell  SafeInferred 

Enduser interface  provides the main functionality for form creation and validation. For an interface for frontend implementation, see View.
 type Formlet v m a = Maybe a > Form v m a
 type Form v m a = FormTree m v m a
 data SomeForm v m = forall a . SomeForm (FormTree Identity v m a)
 (.:) :: Monad m => Text > Form v m a > Form v m a
 text :: Formlet v m Text
 string :: Monad m => Formlet v m String
 stringRead :: (Monad m, Read a, Show a) => v > Formlet v m a
 choice :: (Eq a, Monad m) => [(a, v)] > Formlet v m a
 choice' :: Monad m => [(a, v)] > Maybe Int > Form v m a
 choiceWith :: (Eq a, Monad m) => [(Text, (a, v))] > Formlet v m a
 choiceWith' :: Monad m => [(Text, (a, v))] > Maybe Int > Form v m a
 groupedChoice :: (Eq a, Monad m) => [(Text, [(a, v)])] > Formlet v m a
 groupedChoice' :: Monad m => [(Text, [(a, v)])] > Maybe Int > Form v m a
 groupedChoiceWith :: (Eq a, Monad m) => [(Text, [(Text, (a, v))])] > Formlet v m a
 groupedChoiceWith' :: Monad m => [(Text, [(Text, (a, v))])] > Maybe Int > Form v m a
 bool :: Formlet v m Bool
 file :: Form v m (Maybe FilePath)
 optionalText :: Monad m => Maybe Text > Form v m (Maybe Text)
 optionalString :: Monad m => Maybe String > Form v m (Maybe String)
 optionalStringRead :: (Monad m, Read a, Show a) => v > Maybe a > Form v m (Maybe a)
 check :: Monad m => v > (a > Bool) > Form v m a > Form v m a
 checkM :: Monad m => v > (a > m Bool) > Form v m a > Form v m a
 validate :: Monad m => (a > Result v b) > Form v m a > Form v m b
 validateM :: Monad m => (a > m (Result v b)) > Form v m a > Form v m b
 disable :: Form v m a > Form v m a
 monadic :: m (Form v m a) > Form v m a
 listOf :: Monad m => Formlet v m a > Formlet v m [a]
Documentation
type Form v m a = FormTree m v m aSource
Base type for a form.
The three type parameters are:

v
: the type for textual information, displayed to the user. For example, error messages are of this type.v
stands for view. 
m
: the monad in which validators operate. The classical example is when validating input requires access to a database, in which case thism
should be an instance ofMonadIO
. 
a
: the type of the value returned by the form, used for its Applicative instance.
Valueagnostic Form
Basic forms
stringRead :: (Monad m, Read a, Show a) => v > Formlet v m aSource
Returns a Formlet
for a parseable and serializable value type
choice :: (Eq a, Monad m) => [(a, v)] > Formlet v m aSource
Returns a Formlet
for a value restricted to
the provided list of valuemessage tuples
choiceWith :: (Eq a, Monad m) => [(Text, (a, v))] > Formlet v m aSource
Allows you to assign your own values: these values will be used in the
resulting HTML instead of the default [0 ..]
. This fixes some race
conditions that might otherwise appear, e.g. if new choice items are added to
some database while a user views and submits the form...
choiceWith' :: Monad m => [(Text, (a, v))] > Maybe Int > Form v m aSource
A version of choiceWith
for when there is no good Eq
instance.
groupedChoice :: (Eq a, Monad m) => [(Text, [(a, v)])] > Formlet v m aSource
Returns a Formlet
for named groups of choices.
groupedChoiceWith :: (Eq a, Monad m) => [(Text, [(Text, (a, v))])] > Formlet v m aSource
Allows you to assign your own values: these values will be used in the
resulting HTML instead of the default [0 ..]
. This fixes some race
conditions that might otherwise appear, e.g. if new choice items are added to
some database while a user views and submits the form...
groupedChoiceWith' :: Monad m => [(Text, [(Text, (a, v))])] > Maybe Int > Form v m aSource
Lowlevel support for grouped choice.
Optional forms
optionalText :: Monad m => Maybe Text > Form v m (Maybe Text)Source
Create a text form with an optional default text which returns nothing if no optional text was set, and no input was retrieved.
optionalString :: Monad m => Maybe String > Form v m (Maybe String)Source
Identical to optionalText
, but uses Strings
optionalStringRead :: (Monad m, Read a, Show a) => v > Maybe a > Form v m (Maybe a)Source
Identical to optionalText
for parseable and serializable values.
Validation and transformation
:: Monad m  
=> v  Error message (if fail) 
> (a > Bool)  Validating predicate 
> Form v m a  Form to validate 
> Form v m a  Resulting form 
Validate the results of a form with a simple predicate
Example:
check "Can't be empty" (not . null) (string Nothing)
checkM :: Monad m => v > (a > m Bool) > Form v m a > Form v m aSource
Version of check
which allows monadic validations
validate :: Monad m => (a > Result v b) > Form v m a > Form v m bSource
This is an extension of check
that can be used to apply transformations
that optionally fail
Example: taking the first character of an input string
head' :: String > Result String Char head' [] = Error "Is empty" head' (x : _) = Success x char :: Monad m => Form m String Char char = validate head' (string Nothing)
validateM :: Monad m => (a > m (Result v b)) > Form v m a > Form v m bSource
Version of validate
which allows monadic validations