-- |
-- Module      : Fusion.Plugin.Types
-- Copyright   : (c) 2019 Composewell Technologies
--
-- License     : BSD-3-Clause
-- Maintainer  : pranaysashank@composewell.com
-- Stability   : experimental
-- Portability : GHC

{-# LANGUAGE DeriveDataTypeable #-}

module Fusion.Plugin.Types
    ( Fuse (..)
    )
where

import Data.Data (Data)
import Outputable (Outputable(..), text)

-- | A GHC annotation to inform the plugin to aggressively inline join points
-- that perform a case match on the constructors of the annotated type.
-- Inlining enables case-of-case transformations that would potentially
-- eliminate the constructors.
--
-- This annotation is to be used on types whose constructors are known to be
-- involved in case-of-case transformations enabling stream fusion via
-- elimination of those constructors.
--
-- It is advised to use unique types for intermediate stream state that is to
-- be annotated with 'Fuse'. If the annotated type is also used for some
-- other purpose this annotation may inline code that is not involved in stream
-- fusion and should otherwise not be inlined.
--
-- @
-- {-\# ANN type Step Fuse #-}
-- data Step s a = Yield a s | Skip s | Stop
-- @
data Fuse = Fuse
    deriving (Eq, Data)

instance Outputable Fuse where
    ppr _ = text "Fuse"