PrimControl.hs

module DDC.Core.Salt.Name.PrimControl
        ( PrimControl (..)
        , readPrimControl)
where
import DDC.Data.Pretty
import Control.DeepSeq


-- | Primitive non-returning control flow.
data PrimControl
        -- | Ungraceful failure -- just abort the program.
        --   This is called on internal errors in the runtime system.
        --   There is no further debugging info provided, so you'll need to 
        --   look at the stack trace to debug it.
        = PrimControlFail

        -- | Return from the enclosing function with the given value.
        | PrimControlReturn
        deriving (Eq, Ord, Show)


instance NFData PrimControl where
 rnf !_ = ()


instance Pretty PrimControl where
 ppr pc
  = case pc of
        PrimControlFail         -> text "fail#"
        PrimControlReturn       -> text "return#"


readPrimControl :: String -> Maybe PrimControl
readPrimControl str
 = case str of
        "fail#"         -> Just $ PrimControlFail
        "return#"       -> Just $ PrimControlReturn
        _               -> Nothing