119 lines
4.4 KiB
Haskell
119 lines
4.4 KiB
Haskell
{-# LANGUAGE ImplicitParams #-}
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{-# LANGUAGE LambdaCase #-}
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module Core2Core
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( core2core
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, gmPrep
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-- internal utilities for convenience
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, floatNonStrictCases
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, floatCase
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)
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where
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----------------------------------------------------------------------------------
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import Data.Functor.Foldable
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import Data.Maybe (fromJust)
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import Data.Set (Set)
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import Data.Set qualified as S
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import Data.List
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import Control.Monad.Writer
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import Control.Monad.State.Lazy
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import Control.Arrow ((>>>))
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import Data.Text qualified as T
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import Data.HashMap.Strict (HashMap)
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import Numeric (showHex)
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import Lens.Micro.Platform
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import Core.Syntax
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import Core.Utils
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----------------------------------------------------------------------------------
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core2core :: Program' -> Program'
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core2core p = undefined
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gmPrep :: Program' -> Program'
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gmPrep p = p & appFloater (floatNonStrictCases globals)
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& tagData
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where
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globals = p ^.. programScDefs . each . _lhs . _1
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& S.fromList
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tagData :: Program' -> Program'
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tagData p = let ?dt = p ^. programDataTags
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in p & programRhss %~ cata go where
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go :: (?dt :: HashMap Name (Tag, Int)) => ExprF' Expr' -> Expr'
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go (CaseF e as) = Case e (tagAlts <$> as)
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go x = embed x
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tagAlts :: (?dt :: HashMap Name (Tag, Int)) => Alter' -> Alter'
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tagAlts (Alter (AltData c) bs e) = Alter (AltTag tag) bs e
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where tag = case ?dt ^. at c of
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Just (t,_) -> t
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-- TODO: errorful
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Nothing -> error $ "unknown constructor " <> show c
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tagAlts x = x
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-- | Auxilary type used in @floatNonSrictCases@
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type Floater = StateT [Name] (Writer [ScDef'])
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appFloater :: (Expr' -> Floater Expr') -> Program' -> Program'
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appFloater fl p = p & traverseOf programRhss fl
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& runFloater
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& \ (me,floats) -> me & programScDefs %~ (<>floats)
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runFloater :: Floater a -> (a, [ScDef'])
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runFloater = flip evalStateT ns >>> runWriter
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where
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ns = [ T.pack $ "$nonstrict_case_" ++ showHex n "" | n <- [0..] ]
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-- TODO: formally define a "strict context" and reference that here
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-- the returned ScDefs are guaranteed to be free of non-strict cases.
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floatNonStrictCases :: Set Name -> Expr' -> Floater Expr'
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floatNonStrictCases g = goE
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where
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goE :: Expr' -> Floater Expr'
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goE (Var k) = pure (Var k)
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goE (Lit l) = pure (Lit l)
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goE (Case e as) = pure (Case e as)
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goE (Let Rec bs e) = Let Rec <$> bs' <*> goE e
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where bs' = travBs goE bs
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goE e = goC e
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goC :: Expr' -> Floater Expr'
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-- the only truly non-trivial case: when a case expr is found in a
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-- non-strict context, we float it into a supercombinator, give it a
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-- name consumed from the state, record the newly created sc within the
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-- Writer, and finally return an expression appropriately calling the sc
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goC p@(Case e as) = do
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n <- name
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let (e',sc) = floatCase g n p
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altBodies = (\(Alter _ _ b) -> b) <$> as
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tell [sc]
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goE e
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traverse goE altBodies
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pure e'
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goC (f :$ x) = (:$) <$> goC f <*> goC x
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goC (Let r bs e) = Let r <$> bs' <*> goE e
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where bs' = travBs goC bs
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goC (Lit l) = pure (Lit l)
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goC (Var k) = pure (Var k)
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goC (Con t as) = pure (Con t as)
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name = state (fromJust . uncons)
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-- extract the right-hand sides of a list of bindings, traverse each
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-- one, and return the original list of bindings
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travBs :: (Expr' -> Floater Expr') -> [Binding'] -> Floater [Binding']
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travBs c bs = bs ^.. each . _rhs
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& traverse goC
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& const (pure bs)
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-- when provided with a case expr, floatCase will float the case into a
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-- supercombinator of its free variables. the sc is returned along with an
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-- expression that calls the sc with the necessary arguments
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floatCase :: Set Name -> Name -> Expr' -> (Expr', ScDef')
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floatCase g n c@(Case e as) = (e', sc)
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where
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sc = ScDef n caseFrees c
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caseFrees = S.toList $ freeVariables c `S.difference` g
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e' = foldl App (Var n) (Var <$> caseFrees)
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