Base.hs

module DDC.Source.Tetra.Exp.Base
        ( module DDC.Type.Exp

        -- * Expressions
        , Exp           (..)
        , Lets          (..)
        , Alt           (..)
        , Pat           (..)
        , Cast          (..)

        -- * Witnesses
        , Witness       (..)

        -- * Data Constructors
        , DaCon         (..)

        -- * Witness Constructors
        , WiCon         (..)
        , WbCon         (..))
where
import DDC.Type.Exp
import DDC.Type.Sum     ()
import Control.DeepSeq
import DDC.Core.Exp     
        ( Witness       (..)
        , WiCon         (..)
        , WbCon         (..)
        , Pat           (..)
        , DaCon         (..))


-- | Well-typed expressions have types of kind `Data`.
data Exp a n
        ---------------------------------------------------
        -- Core Language Constructs.
        --   These are also in the core language, and after desugaring only
        --   these constructs are used.
        --
        -- | Value variable   or primitive operation.
        = XVar      !a !(Bound n)

        -- | Data constructor or literal.
        | XCon      !a !(DaCon n)

        -- | Type abstraction (level-1).
        | XLAM      !a !(Bind n)   !(Exp a n)

        -- | Value and Witness abstraction (level-0).
        | XLam      !a !(Bind n)   !(Exp a n)

        -- | Application.
        | XApp      !a !(Exp a n)  !(Exp a n)

        -- | Possibly recursive bindings.
        | XLet      !a !(Lets a n) !(Exp a n)

        -- | Case branching.
        | XCase     !a !(Exp a n)  ![Alt a n]

        -- | Type cast.
        | XCast     !a !(Cast a n) !(Exp a n)

        -- | Type can appear as the argument of an application.
        | XType     !a !(Type n)

        -- | Witness can appear as the argument of an application.
        | XWitness  !a !(Witness a n)


        ---------------------------------------------------
        -- Sugar Constructs.
        --  These constructs are eliminated by the desugarer.
        --
        -- | Some expressions and infix operators that need to be resolved into
        --   proper function applications.
        | XDefix    !a [Exp a n]

        -- | Use of a naked infix operator, like in 1 + 2.
        --   INVARIANT: only appears in the list of an XDefix node.
        | XInfixOp  !a String

        -- | Use of an infix operator as a plain variable, like in (+) 1 2.
        --   INVARIANT: only appears in the list of an XDefix node.
        | XInfixVar !a String
        deriving (Show, Eq)


-- | Possibly recursive bindings.
data Lets a n
        -- | Non-recursive let-binding.
        = LLet     !(Bind n) !(Exp a n)

        -- | Recursive let bindings.
        | LRec     ![(Bind n, Exp a n)]

        -- | Bind a local region variable,
        --   and witnesses to its properties.
        | LPrivate ![Bind n] !(Maybe (Type n)) ![Bind n]
        deriving (Show, Eq)


-- | Case alternatives.
data Alt a n
        = AAlt !(Pat n) !(Exp a n)
        deriving (Show, Eq)


-- | Type casts.
data Cast a n
        -- | Weaken the effect of an expression.
        --   The given effect is added to the effect
        --   of the body.
        = CastWeakenEffect  !(Effect n)
        
        -- | Purify the effect (action) of an expression.
        | CastPurify !(Witness a n)

        -- | Box a computation, 
        --   capturing its effects in the S computation type.
        | CastBox

        -- | Run a computation,
        --   releasing its effects into the environment.
        | CastRun
        deriving (Show, Eq)

        
-- NFData ---------------------------------------------------------------------
instance (NFData a, NFData n) => NFData (Exp a n) where
 rnf xx
  = case xx of
        XVar      a u      -> rnf a `seq` rnf u
        XCon      a dc     -> rnf a `seq` rnf dc
        XLAM      a b x    -> rnf a `seq` rnf b   `seq` rnf x
        XLam      a b x    -> rnf a `seq` rnf b   `seq` rnf x
        XApp      a x1 x2  -> rnf a `seq` rnf x1  `seq` rnf x2
        XLet      a lts x  -> rnf a `seq` rnf lts `seq` rnf x
        XCase     a x alts -> rnf a `seq` rnf x   `seq` rnf alts
        XCast     a c x    -> rnf a `seq` rnf c   `seq` rnf x
        XType     a t      -> rnf a `seq` rnf t
        XWitness  a w      -> rnf a `seq` rnf w
        XDefix    a xs     -> rnf a `seq` rnf xs
        XInfixOp  a s      -> rnf a `seq` rnf s
        XInfixVar a s      -> rnf a `seq` rnf s


instance (NFData a, NFData n) => NFData (Cast a n) where
 rnf cc
  = case cc of
        CastWeakenEffect e      -> rnf e
        CastPurify w            -> rnf w
        CastBox                 -> ()
        CastRun                 -> ()


instance (NFData a, NFData n) => NFData (Lets a n) where
 rnf lts
  = case lts of
        LLet b x                -> rnf b `seq` rnf x
        LRec bxs                -> rnf bxs
        LPrivate bs1 mR bs2     -> rnf bs1  `seq` rnf mR `seq` rnf bs2


instance (NFData a, NFData n) => NFData (Alt a n) where
 rnf aa
  = case aa of
        AAlt w x                -> rnf w `seq` rnf x