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{-# LANGUAGE UndecidableInstances #-}

module Feldspar.Core.Constructs.Error where



import Language.Syntactic
import Language.Syntactic.Interpretation.Semantics
import Language.Syntactic.Constructs.Binding

import Feldspar.Range
import Feldspar.Core.Types
import Feldspar.Core.Interpretation



data Error a
  where
    Undefined :: Type a => Error (Full a)
    Assert    :: Type a => String -> Error (Bool :-> a :-> Full a)

instance WitnessCons Error
  where
    witnessCons Undefined  = ConsWit
    witnessCons (Assert _) = ConsWit

instance WitnessSat Error
  where
    type SatContext Error = TypeCtx
    witnessSat Undefined  = SatWit
    witnessSat (Assert _) = SatWit

instance MaybeWitnessSat TypeCtx Error
  where
    maybeWitnessSat = maybeWitnessSatDefault

instance Semantic Error
  where
    semantics Undefined    = Sem "undefined" undefined
    semantics (Assert msg) = Sem "assert"
        (\cond a -> if cond then a else error ("Assert failed: " ++ msg))

instance Render Error
  where
    render Undefined    = "undefined"
    render (Assert msg) = "assert " ++ show msg

instance ExprEq   Error where exprEq = exprEqSem; exprHash = exprHashSem
instance ToTree   Error
instance Eval     Error where evaluate = evaluateSem
instance EvalBind Error where evalBindSym = evalBindSymDefault
instance SizeProp Error where sizeProp = sizePropDefault
instance Sharable Error

instance AlphaEq dom dom dom env => AlphaEq Error Error dom env
  where
    alphaEqSym = alphaEqSymDefault

instance (Error :<: dom, Optimize dom dom) => Optimize Error dom
  where
    constructFeatUnOpt = constructFeatUnOptDefault