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SI-7038 Deskolemize harder #3

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SI-7038 Deskolemize harder #3

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SI-7308 A pending test.
retronym Jan 29, 2013
fe99eb3
SI-7038 Deskolemize harder
retronym Jan 29, 2013
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2 changes: 2 additions & 0 deletions src/reflect/scala/reflect/internal/ExistentialsAndSkolems.scala
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Expand Up @@ -41,6 +41,8 @@ trait ExistentialsAndSkolems {
def apply(tp: Type): Type = tp match {
case TypeRef(pre, sym, args) if sym.isTypeSkolem && (tparams contains sym.deSkolemize) =>
mapOver(typeRef(NoPrefix, sym.deSkolemize, args))
case TypeRef(pre, sym, args) if sym.isAliasType =>
mapOver(tp.normalize)
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i'd dealias instead of normalize (and only if !(tp.dealias =:= tp) -- i.e., when arguments are supplied so that we don't have to eta-expand to a polytype)

otherwise, looks good

EDIT: I think tp.dealias match { ... } should work, no need for the case for alias types

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Lukas's latest PR actually removed this custom TypeMap in favour of a straight restpe.substSyms(skolems, tparams). Which got me to thinking about how this version might be expressed in the same way; which other custom type maps could be expressed in the same way, etc.

What I'm thinking of is dealiasLocals(method, restpe).substSyms(skolems, tparams), where dealiasLocals would dealias any types aliases that are local to the method. Does that sound like a reasonable approach? How would I build such a thing?

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the problem is sym.deSkolemize doesn't have an inverse, so you can't easily determine the skolems list
for sym in skolems. TR(pre, sym, as) -> TR(NoPrefix, sym.deSkolemize, args)
skolems = {sym | sym.deSkolemize in tparams}

the only way I can see to express this as a substitution is to

  • generalize the from/to arguments of the substitution to a function
  • or get a list of all symbols in the type to transform

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Here's what @lrytz is up to.

      /* tparams already have symbols (created in enterDefDef/completerOf), namely the skolemized ones (created
       * by the PolyTypeCompleter constructor, and assigned to tparams). reenterTypeParams enters the type skolems
       * into scope and returns the non-skolems.
        */

      val tparamSyms = typer.reenterTypeParams(tparams)
       val tparamSkolems = tparams.map(_.symbol)

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I think that still goes from skolem to non-skolem
i don't know how to go from non-skolem to (original) skolem

case _ =>
mapOver(tp)
}
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25 changes: 25 additions & 0 deletions test/files/run/t7308.check
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@@ -0,0 +1,25 @@
Type in expressions to have them evaluated.
Type :help for more information.

scala> def foo[S] = { type X = List[S]; List():X }
foo: [S]=> List[S]

scala> val li = foo[Int]
li: List[Int] = List()

scala> li: List[Int]
res0: List[Int] = List()

scala> type TL = List[Int]
defined type alias TL

scala> def foo = null: TL
foo: TL

scala> def foo = {type TL=List[Int]; null: TL}
foo: TL

scala> foo: List[Int]
res1: List[Int] = null

scala>
14 changes: 14 additions & 0 deletions test/files/run/t7308.scala
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@@ -0,0 +1,14 @@
import scala.tools.partest.ReplTest

object Test extends ReplTest {

override def code = """
def foo[S] = { type X = List[S]; List():X }
val li = foo[Int]
li: List[Int]
type TL = List[Int]
def foo = null: TL
def foo = {type TL=List[Int]; null: TL}
foo: List[Int]
""".trim
}