-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Template haskell utilities for helping with deserialization etc. of existential types
--   
--   instance-map provides Template Haskell functions that help go from
--   serialized values with value-level type witnesses (i.e. TypeRep
--   values) to existential types containing type-level evidence of
--   membership in a type class. It is useful for dealing with serialized
--   values when only membership in a certain class (and not the
--   monomorphic type) is known at the site of deserialization.
@package instance-map
@version 0.1.0.0

module Type.InstanceMap.TH

-- | When used as a declaration splice, this function will create three
--   declarations:
--   
--   <ul>
--   <li>A data instance <a>Some</a> <i>ClassName</i> with a single
--   constructor Some<i>ClassName</i></li>
--   <li>A value named mapOf<i>ClassName</i>, which has type</li>
--   </ul>
--   
--   <pre>
--   <a>Map</a> <a>TypeRep</a> <i>InputType</i> -&gt; <a>Some</a> <i>Class</i>
--   </pre>
--   
--   <ul>
--   <li>A helper function getSome<i>ClassName</i> with signature</li>
--   </ul>
--   
--   <pre>
--   <a>TypeRep</a> -&gt; <i>InputType</i> -&gt; <a>Maybe</a> (<a>Some</a> <i>Class</i>)
--   </pre>
--   
--   The four arguments to this function are:
--   
--   <ol>
--   <li>A TypeRep indicating what monomorphic type we should try to
--   decode</li>
--   <li>The name of the type that is the argument to the decoder function.
--   Often ''ByteString or ''Aeson.Value.</li>
--   <li>The name of a monad type with an instance of MonadFail that the
--   functional expression uses to wrap the return value. Often
--   ''Maybe.</li>
--   <li>A quasiquoted expression for a function that takes an argument of
--   the type named by (2) and has a polymorphic return type wrapped in the
--   monad (3).</li>
--   </ol>
--   
--   For example, for JSON the call generally be:
--   
--   <pre>
--   $(mkMap ''MyClass ''Value ''Result [|fromJSON|])
--   </pre>
mkMap :: ClassName -> InputTypeName -> OutputWrapperName -> ExpQ -> Q [Dec]

-- | Like <a>mkMap</a> but with user-provided <a>Options</a>
mkMapWithOpts :: Options -> ClassName -> InputTypeName -> OutputWrapperName -> ExpQ -> Q [Dec]
defaultOptions :: Options
type ClassName = Name
type InputTypeName = Name
type OutputWrapperName = Name
data Options
Options :: Int -> Bool -> ExpQ -> Name -> Options

-- | How deep to traverse the tree of instance contexts when attempting to
--   find monomorphic types that are members of the class. Default is 2.
--   
--   For instance, if we have declarations like:
--   
--   <pre>
--   data NumWithS n = NumWithS String n
--   instance (Num a) =&gt; Num (NumWithS a)
--   </pre>
--   
--   with maxDepth set to 2, then NumWithS Int and NumWithS (NumWithS Int)
--   would both be found but NumWithS (NumWithS (NumWithS Int)) would not
--   be.
[maxDepth] :: Options -> Int

-- | Whether to produce lots of debugging output. Default False.
[verbose] :: Options -> Bool
[witnessGenerator] :: Options -> ExpQ
[witnessTypeName] :: Options -> Name

module Type.InstanceMap