Safe Haskell	Safe
Language	Haskell2010

Servant.Server.Internal.Context

Contents

support for named subcontexts

Synopsis

Documentation

data Context contextTypes where Source #

Contexts are used to pass values to combinators. (They are not meant to be used to pass parameters to your handlers, i.e. they should not replace any custom ReaderT-monad-stack that you're using with Enter.) If you don't use combinators that require any context entries, you can just use serve as always.

If you are using combinators that require a non-empty Context you have to use serveWithContext and pass it a Context that contains all the values your combinators need. A Context is essentially a heterogenous list and accessing the elements is being done by type (see getContextEntry). The parameter of the type Context is a type-level list reflecting the types of the contained context entries. To create a Context with entries, use the operator (:.):

>>> :type True :. () :. EmptyContext
True :. () :. EmptyContext :: Context '[Bool, ()]

Constructors

EmptyContext :: Context '[]
(:.) :: x -> Context xs -> Context (x ': xs) infixr 5

Instances

(Eq a, Eq (Context as)) => Eq (Context ((:) * a as)) Source #
Methods (==) :: Context ((* ': a) as) -> Context ((* ': a) as) -> Bool # (/=) :: Context ((* ': a) as) -> Context ((* ': a) as) -> Bool #
Eq (Context ([] *)) Source #
Methods (==) :: Context [] -> Context [] -> Bool # (/=) :: Context [] -> Context [] -> Bool #
(Show a, Show (Context as)) => Show (Context ((:) * a as)) Source #
Methods showsPrec :: Int -> Context ((* ': a) as) -> ShowS # show :: Context ((* ': a) as) -> String # showList :: [Context ((* ': a) as)] -> ShowS #
Show (Context ([] *)) Source #
Methods showsPrec :: Int -> Context [] -> ShowS # show :: Context [] -> String # showList :: [Context [*]] -> ShowS #

class HasContextEntry context val where Source #

This class is used to access context entries in Contexts. getContextEntry returns the first value where the type matches:

>>> getContextEntry (True :. False :. EmptyContext) :: Bool
True

If the Context does not contain an entry of the requested type, you'll get an error:

>>> getContextEntry (True :. False :. EmptyContext) :: String
...
...No instance for (HasContextEntry '[] [Char])
...

Minimal complete definition

getContextEntry

Methods

getContextEntry :: Context context -> val Source #

Instances

HasContextEntry ((:) * val xs) val Source #
Methods getContextEntry :: Context ((* ': val) xs) -> val Source #
HasContextEntry xs val => HasContextEntry ((:) * notIt xs) val Source #
Methods getContextEntry :: Context ((* ': notIt) xs) -> val Source #

support for named subcontexts

data NamedContext name subContext Source #

Normally context entries are accessed by their types. In case you need to have multiple values of the same type in your Context and need to access them, we provide NamedContext. You can think of it as sub-namespaces for Contexts.

Constructors

NamedContext (Context subContext)

descendIntoNamedContext :: forall context name subContext. HasContextEntry context (NamedContext name subContext) => Proxy (name :: Symbol) -> Context context -> Context subContext Source #

descendIntoNamedContext allows you to access NamedContexts. Usually you won't have to use it yourself but instead use a combinator like WithNamedContext.

This is how descendIntoNamedContext works:

>>> :set -XFlexibleContexts
>>> let subContext = True :. EmptyContext
>>> :type subContext
subContext :: Context '[Bool]
>>> let parentContext = False :. (NamedContext subContext :: NamedContext "subContext" '[Bool]) :. EmptyContext
>>> :type parentContext
parentContext :: Context '[Bool, NamedContext "subContext" '[Bool]]
>>> descendIntoNamedContext (Proxy :: Proxy "subContext") parentContext :: Context '[Bool]
True :. EmptyContext