Expr.hs

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-- Copyright © 2011 National Institute of Aerospace / Galois, Inc.
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{-# LANGUAGE GADTs, ExistentialQuantification #-}

module Copilot.Core.Expr
  ( Id
  , Name
  , Expr (..)
  , UExpr (..)
  , DropIdx
  , Tag
  ) where

import Copilot.Core.Operators (Op1, Op2, Op3)
import Copilot.Core.Type (Type)
import Data.Word (Word16)

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-- | A stream identifier.
type Id = Int

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-- | A name of a trigger, an external variable, or an external function.
type Name = String

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-- | An index for the drop operator.
type DropIdx = Word16

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-- | A unique tag for external arrays/function calls.
type Tag = Int

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data Expr a where
  Const
    :: Type a
    -> a
    -> Expr a
  Drop
    :: Type a
    -> DropIdx
    -> Id
    -> Expr a
  Local
    :: Type a
    -> Type b
    -> Name
    -> Expr a
    -> Expr b
    -> Expr b
  Var
    :: Type a
    -> Name
    -> Expr a
  ExternVar
    :: Type a
    -> Name
    -> Expr a
  ExternFun
    :: Type a
    -> Name
    -> [UExpr]
    -> Maybe Tag
    -> Expr a
  ExternArray
    :: Integral a
    => Type a
    -> Type b
    -> Name
    -> Expr a
    -> Maybe Tag
    -> Expr b
  Op1
    :: Op1 a b
    -> Expr a
    -> Expr b
  Op2
    :: Op2 a b c
    -> Expr a
    -> Expr b
    -> Expr c
  Op3
    :: Op3 a b c d
    -> Expr a
    -> Expr b
    -> Expr c
    -> Expr d

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-- | A untyped expression (no phantom type).
data UExpr = forall a . UExpr
  { uExprType :: Type a
  , uExprExpr :: Expr a }