Documentation

A marker to tell the core plugin to replace the implementation of a top-level function by a corresponding class data constructor (wrapped into Dict).

Example:

class BarClass a => FooClass a where
  fooFun1 :: a -> a -> Int
  fooFun2 :: a -> Bool

{-# ANN deriveFooClass ClassDict #-}
deriveFooClass :: forall a . BarClass a
               => (a -> a -> Int)
               -> (a -> Bool)
               -> Dict (FooClass a)
deriveFooClass = deriveFooClass

That is, the plugin replaces the RHS of deriveFooClass function with classDataCon wrapped by bareToDict.

Note:

• The plugin requires you to create a dummy function deriveFooClass and annotate it with ClassDict instead of automatically creating this function for you; this way, the function is visible during type checking: you can use it in the same module (avoiding orphans) and you see its type signature.
• You have to provide a correct signature for deriveFooClass function; the plugin compares this signature against visible classes and their constructors. An incorrect signature will result in a compile-time error.
• The dummy implementation deriveFooClass = deriveFooClass is used here to prevent GHC from inlining the function before the plugin can replace it. But you can implement in any way you like at your own risk.

Run ClassDict plugin pass

Reference to the plugin environment variables.

Init the CorePluginM environment and save it to IORef.