module DDC.Core.Tetra.Transform.Curry.CallThunk
        (makeCallThunk)
where
import DDC.Core.Tetra.Transform.Curry.Error
import DDC.Core.Tetra.Prim
import DDC.Core.Exp.Annot
import qualified DDC.Core.Call                          as Call
import qualified DDC.Core.Tetra.Compounds               as C
import qualified DDC.Type.Transform.Instantiate         as T

-- | Apply a thunk to some more arguments.
--
--   The arguments must have be values, with type of kind `Data`.
--   If this is not true then `Nothing`.
--
makeCallThunk
        :: Exp () Name                  -- ^ Functional expression to apply.
        -> Type Name                    -- ^ Type of functional expression.
        -> [Call.Elim () Name]          -- ^ Eliminators for applicatoin.
        -> Either Error (Maybe (Exp () Name))

makeCallThunk xF tF esArgs

 -- Split the eliminators according to the standard call pattern.
 | Just (esType, esValue, esRun)  
                <- Call.splitStdCallElims esArgs
 , Just tF_inst <- T.instantiateTs tF [t | Call.ElimType _ _ t <- esType]
 = let  
        (tsParam, tResult)       = C.takeTFunArgResult tF_inst

        -- Split the value parameters into ones applied to the thunk,
        -- and the ones that form part of its resulting type. 
        (tsParamArg, tsParamClo) = splitAt (length esValue) tsParam

        -- Build the type of the returned closure.
        --   Splitting the type like this assumes that the thunk 
        --   we're applying has a monomorphic type, which is true
        --   for thunked supers with standard calling convention as
        --   the types of these are all prenex.
        tResultClo      = C.tFunOfParamResult tsParamClo tResult

        xsArgs          = [ x | Call.ElimValue _ x <- esValue] 

   in  return 
         $ Just 
         $ makeRuns    () (length esRun)
         $ C.xFunApply () tsParamArg tResultClo 
                (xApps () xF [XType () t | Call.ElimType _ _ t <- esType])
                xsArgs

 | otherwise
 = return $ Nothing