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Implement match type amendment: extractors follow aliases and singletons
This implements the change proposed in scala/improvement-proposals#84. The added pos test case presents motivating examples, the added neg test cases demonstrate that errors are correctly reported when cycles are present. The potential for cycle is no worse than with the existing extraction logic as demonstrated by the existing test in `tests/neg/mt-deskolemize.scala`.
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Original file line number | Diff line number | Diff line change |
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trait Expr: | ||
type Value | ||
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object Expr: | ||
type Of[V] = Expr { type Value = V } | ||
type ExtractValue[F <: Expr] = F match | ||
case Expr.Of[v] => v | ||
import Expr.ExtractValue | ||
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class Prim extends Expr: | ||
type Value = Alias | ||
type Alias = BigInt | ||
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class VecExpr[E <: Expr] extends Expr: | ||
type Value = Vector[ExtractValue[E]] | ||
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trait Description: | ||
type Elem <: Tuple | ||
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trait ProdExpr extends Expr: | ||
val description: Description | ||
type Value = Tuple.Map[description.Elem, [X] =>> ExtractValue[X & Expr]] | ||
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class MyExpr1 extends ProdExpr: | ||
final val description = new Description: | ||
type Elem = (VecExpr[Prim], Prim) | ||
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class MyExpr2 extends ProdExpr: | ||
final val description = new Description: | ||
type Elem = (VecExpr[VecExpr[MyExpr1]], Prim) | ||
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trait ProdExprAlt[T <: Tuple] extends Expr: | ||
type Value = Tuple.Map[T, [X] =>> ExtractValue[X & Expr]] | ||
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class MyExpr3 extends ProdExprAlt[(Prim, VecExpr[Prim], Prim)] | ||
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trait Constable[E <: Expr]: | ||
def lit(v: ExtractValue[E]): E | ||
object Constable: | ||
given [E <: Expr]: Constable[E] = ??? | ||
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object Test: | ||
def fromLiteral[E <: Expr : Constable](v: ExtractValue[E]): E = | ||
summon[Constable[E]].lit(v) | ||
val a: Prim = fromLiteral(1) | ||
val b: VecExpr[Prim] = fromLiteral(Vector(1)) | ||
val c: MyExpr1 = fromLiteral((Vector(1), 1)) | ||
val d: MyExpr2 = fromLiteral(Vector(Vector((Vector(1), 1))), 2) | ||
val e: MyExpr3 = fromLiteral((1, Vector(1), 1)) | ||
val f: ProdExprAlt[(MyExpr1, VecExpr[MyExpr3])] = fromLiteral: | ||
( | ||
(Vector(1), 1), | ||
Vector((1, Vector(1), 1), (2, Vector(1), 2)) | ||
) | ||
val g: Expr { type Alias = Int; type Value = Alias } = fromLiteral(1) |