Happstack.Foundation

happstack-foundation provides a type-safe environment for Haskell web development. It builds on top of:

• happstack-server - an HTTP server
• HSP - HTML Templating
• web-routes - type-safe URL routing
• reform - type-safe form composition and validation
• acid-state - native Haskell persistent database

An example application can be found here:

http://patch-tag.com/r/mae/happstack/snapshot/current/content/pretty/happstack-foundation/examples/ControlV/Main.hs

A screencast can be found here:

http://www.youtube.com/watch?v=7Wmszk4wZxQ

happstack-foundation itself is not yet documented in the Happstack Crash Course. However, all of the components that it uses are:

http://www.happstack.com/docs/crashcourse/index.html

Configuration

data AcidConfig st where

configuration information for our acid-state database

Constructors

AcidLocal :: (IsAcidic st, Typeable st) => Maybe FilePath -> st -> AcidConfig (AcidState st)

AcidUsing :: st -> AcidConfig st

data FoundationConf

configuration for server

Constructors

FoundationConf

Fields

httpConf :: Conf

bodyPolicy :: BodyPolicy

defaultConf :: FoundationConf

configuration

Type Aliases

type FoundationT url acidState requestState m = XMLGenT (FoundationT' url acidState requestState m)

the FoundationT monad

• url - the type-safe URL route type
• acidState - the type of the state value stored in acid-state
• requestState - a per-request state value that the developer can getsetmodify
• m - inner monad

see also: whereami, getRequestState, setRequestState, modifyRequestState, simpleApp

type FoundationT' url acidState requestState m = RouteT url (StateT (AppState url acidState requestState) (ServerPartT m))

similar to the FoundationT' type alias, but without the XMLGenT wrapper. This variant is most often used in class constraints.

type FoundationForm url acidState requestState m = Form (FoundationT url acidState requestState m) [Input] AppError [FoundationT url acidState requestState m XML] ()

FoundationForm is an alias for working with reform based Forms

FoundationT functions

whereami :: (Functor m, Monad m) => FoundationT url acidState requestState m url

returns the decoded url from the Request

getRequestState :: (Functor m, MonadState (AppState url acidState requestState) m) => m requestState

get the requestState value

setRequestState :: (Functor m, MonadState (AppState url acidState requestState) m) => requestState -> m ()

set the requestState value

modifyRequestState :: MonadState (AppState url acidState requestState) m => (requestState -> requestState) -> m ()

set the requestState value

HTML Template

defaultTemplate :: (Functor m, Monad m, XMLGenerator (FoundationT' url acidState requestState m), EmbedAsChild (FoundationT' url acidState requestState m) body, EmbedAsChild (FoundationT' url acidState requestState m) headers, XMLType (FoundationT' url acidState requestState m) ~ XML) => Text -> headers -> body -> FoundationT url acidState requestState m XML

default page template

acid-state

class HasAcidState m st where

HasAcidState provides a single method getAcidState which can be used to retrieve an AcidState handle from the current monad.

Methods

getAcidState :: m (AcidState st)

Instances

HasAcidState (FoundationT' url acid reqSt m) acidSt => HasAcidState (XMLGenT (FoundationT' url acid reqSt m)) acidSt

(Functor m, Monad m) => HasAcidState (FoundationT url (AcidState acidState) requestState m) acidState

query :: forall event m. (Functor m, MonadIO m, QueryEvent event, HasAcidState m (EventState event)) => event -> m (EventResult event)

wrapper around query from acid-state

This variant automatically gets the AcidState handle from the monad

update :: forall event m. (Functor m, MonadIO m, UpdateEvent event, HasAcidState m (EventState event)) => event -> m (EventResult event)

wrapper around update from acid-state

This variant automatically gets the AcidState handle from the monad

getAcidSt :: (Functor m, MonadState (AppState url acidState requestState) m) => m acidState

running

simpleApp

Arguments

:: (ToMessage a, PathInfo url, Monad m)

=> (forall r. m r -> IO r)

function to flatten inner monad

-> FoundationConf

Conf to pass onto simpleHTTP

-> AcidConfig acidState

AcidState configuration

-> requestState

initial requestState value

-> url

default URL (ie, what does / map to)

-> Text

-> (url -> FoundationT url acidState requestState m a)

handler

-> IO ()

run the application

starts the database, listens for requests, etc.

re-exports

class Typeable a => Data a where

The Data class comprehends a fundamental primitive gfoldl for folding over constructor applications, say terms. This primitive can be instantiated in several ways to map over the immediate subterms of a term; see the gmap combinators later in this class. Indeed, a generic programmer does not necessarily need to use the ingenious gfoldl primitive but rather the intuitive gmap combinators. The gfoldl primitive is completed by means to query top-level constructors, to turn constructor representations into proper terms, and to list all possible datatype constructors. This completion allows us to serve generic programming scenarios like read, show, equality, term generation.

The combinators gmapT, gmapQ, gmapM, etc are all provided with default definitions in terms of gfoldl, leaving open the opportunity to provide datatype-specific definitions. (The inclusion of the gmap combinators as members of class Data allows the programmer or the compiler to derive specialised, and maybe more efficient code per datatype. Note: gfoldl is more higher-order than the gmap combinators. This is subject to ongoing benchmarking experiments. It might turn out that the gmap combinators will be moved out of the class Data.)

Conceptually, the definition of the gmap combinators in terms of the primitive gfoldl requires the identification of the gfoldl function arguments. Technically, we also need to identify the type constructor c for the construction of the result type from the folded term type.

In the definition of gmapQx combinators, we use phantom type constructors for the c in the type of gfoldl because the result type of a query does not involve the (polymorphic) type of the term argument. In the definition of gmapQl we simply use the plain constant type constructor because gfoldl is left-associative anyway and so it is readily suited to fold a left-associative binary operation over the immediate subterms. In the definition of gmapQr, extra effort is needed. We use a higher-order accumulation trick to mediate between left-associative constructor application vs. right-associative binary operation (e.g., (:)). When the query is meant to compute a value of type r, then the result type withing generic folding is r -> r. So the result of folding is a function to which we finally pass the right unit.

With the -XDeriveDataTypeable option, GHC can generate instances of the Data class automatically. For example, given the declaration

 data T a b = C1 a b | C2 deriving (Typeable, Data)

GHC will generate an instance that is equivalent to

 instance (Data a, Data b) => Data (T a b) where
     gfoldl k z (C1 a b) = z C1 `k` a `k` b
     gfoldl k z C2       = z C2

     gunfold k z c = case constrIndex c of
                         1 -> k (k (z C1))
                         2 -> z C2

     toConstr (C1 _ _) = con_C1
     toConstr C2       = con_C2

     dataTypeOf _ = ty_T

 con_C1 = mkConstr ty_T "C1" [] Prefix
 con_C2 = mkConstr ty_T "C2" [] Prefix
 ty_T   = mkDataType "Module.T" [con_C1, con_C2]

This is suitable for datatypes that are exported transparently.

Methods

gfoldl

Arguments

:: (forall d b. Data d => c (d -> b) -> d -> c b)

defines how nonempty constructor applications are folded. It takes the folded tail of the constructor application and its head, i.e., an immediate subterm, and combines them in some way.

-> (forall g. g -> c g)

defines how the empty constructor application is folded, like the neutral / start element for list folding.

-> a

structure to be folded.

-> c a

result, with a type defined in terms of a, but variability is achieved by means of type constructor c for the construction of the actual result type.

Left-associative fold operation for constructor applications.

The type of gfoldl is a headache, but operationally it is a simple generalisation of a list fold.

The default definition for gfoldl is const id, which is suitable for abstract datatypes with no substructures.

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c a

Unfolding constructor applications

toConstr :: a -> Constr

Obtaining the constructor from a given datum. For proper terms, this is meant to be the top-level constructor. Primitive datatypes are here viewed as potentially infinite sets of values (i.e., constructors).

dataTypeOf :: a -> DataType

The outer type constructor of the type

dataCast1 :: Typeable1 t => (forall d. Data d => c (t d)) -> Maybe (c a)

Mediate types and unary type constructors. In Data instances of the form T a, dataCast1 should be defined as gcast1.

The default definition is const Nothing, which is appropriate for non-unary type constructors.

dataCast2 :: Typeable2 t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a)

Mediate types and binary type constructors. In Data instances of the form T a b, dataCast2 should be defined as gcast2.

The default definition is const Nothing, which is appropriate for non-binary type constructors.

gmapT :: (forall b. Data b => b -> b) -> a -> a

A generic transformation that maps over the immediate subterms

The default definition instantiates the type constructor c in the type of gfoldl to an identity datatype constructor, using the isomorphism pair as injection and projection.

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r

A generic query with a left-associative binary operator

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r

A generic query with a right-associative binary operator

gmapQ :: (forall d. Data d => d -> u) -> a -> [u]

A generic query that processes the immediate subterms and returns a list of results. The list is given in the same order as originally specified in the declaratoin of the data constructors.

gmapQi :: Int -> (forall d. Data d => d -> u) -> a -> u

A generic query that processes one child by index (zero-based)

gmapM :: Monad m => (forall d. Data d => d -> m d) -> a -> m a

A generic monadic transformation that maps over the immediate subterms

The default definition instantiates the type constructor c in the type of gfoldl to the monad datatype constructor, defining injection and projection using return and >>=.

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a

Transformation of at least one immediate subterm does not fail

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a

Transformation of one immediate subterm with success

Instances

Data Bool

Data Char

Data Double

Data Float

Data Int

Data Int8

Data Int16

Data Int32

Data Int64

Data Integer

Data Ordering

Data Word

Data Word8

Data Word16

Data Word32

Data Word64

Data ()

Data Handle

Data DataType

Data ThreadId

Data TypeRep

Data TyCon

Data Text

Data Text

Data Method

Data LocalTime

Data ZonedTime

Data a => Data [a]

(Data a, Integral a) => Data (Ratio a)

Typeable a => Data (StablePtr a)

Typeable a => Data (IO a)

Typeable a => Data (Ptr a)

Typeable a => Data (ForeignPtr a)

Typeable a => Data (STM a)

Typeable a => Data (TVar a)

Typeable a => Data (IORef a)

Typeable a => Data (MVar a)

Data a => Data (Maybe a)

Data a => Data (Errors a)

(Data a, Data b) => Data (a -> b)

(Data a, Data b) => Data (Either a b)

(Data a, Data b) => Data (a, b)

(Typeable s, Typeable a) => Data (ST s a)

(Typeable a, Data b, Ix a) => Data (Array a b)

(Data a, Data b, Data c) => Data (a, b, c)

(Data a, Data b, Data c, Data d) => Data (a, b, c, d)

(Data a, Data b, Data c, Data d, Data e) => Data (a, b, c, d, e)

(Data a, Data b, Data c, Data d, Data e, Data f) => Data (a, b, c, d, e, f)

(Data a, Data b, Data c, Data d, Data e, Data f, Data g) => Data (a, b, c, d, e, f, g)

class Typeable a where

The class Typeable allows a concrete representation of a type to be calculated.

Methods

typeOf :: a -> TypeRep

Takes a value of type a and returns a concrete representation of that type. The value of the argument should be ignored by any instance of Typeable, so that it is safe to pass undefined as the argument.

Instances

Typeable Bool

Typeable Char

Typeable Double

Typeable Float

Typeable Int

Typeable Int8

Typeable Int16

Typeable Int32

Typeable Int64

Typeable Integer

Typeable Ordering

Typeable RealWorld

Typeable Word

Typeable Word8

Typeable Word16

Typeable Word32

Typeable Word64

Typeable ()

Typeable Socket

Typeable DataType

Typeable ThreadId

Typeable TypeRep

Typeable TyCon

Typeable Text

Typeable Text

Typeable Method

Typeable RsFlags

Typeable Input

Typeable Response

Typeable Request

Typeable RqBody

Typeable SocketOption

Typeable ShutdownCmd

Typeable AddrInfoFlag

Typeable AddrInfo

Typeable NameInfoFlag

Typeable SocketStatus

Typeable SocketType

Typeable PortNumber

Typeable SockAddr

Typeable LocalTime

Typeable ZonedTime

(Typeable1 s, Typeable a) => Typeable (s a)

One Typeable instance for all Typeable1 instances

module Control.Applicative

module Control.Monad.Reader

module Control.Monad.State

module Data.SafeCopy

module Data.Acid

module Happstack.Server

module HSP

module Web.Routes

module Web.Routes.Happstack

module Web.Routes.TH

module Text.Reform

module Text.Reform.Happstack

module Text.Reform.HSP.Text