Tests for strict and lazy maps over boxes

Author: odersky

tests/neg-custom-args/captures/boxmap.check

@@ -0,0 +1,10 @@
+-- [E007] Type Mismatch Error: boxmap.scala:15:2 -------------------------------
+15 |  () => b[Box[B]]((x: A) => box(f(x)))
+   |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |  Found:    (() => Box[B]) retains b retains f
+   |  Required: () => Box[B]
+   |
+   |  where:    B is a type in method lazymap with bounds <: Top
+
+longer explanation available when compiling with `-explain`
+1 error found

tests/neg-custom-args/captures/boxmap.scala

@@ -0,0 +1,15 @@
+type Top = Any retains *
+class Cap extends Retains[*]
+
+infix type ==> [A, B] = (A => B) retains *
+
+type Box[+T <: Top] = [K <: Top] => (T ==> K) => K
+
+def box[T <: Top](x: T): Box[T] =
+  [K <: Top] => (k: T ==> K) => k(x)
+
+def map[A <: Top, B <: Top](b: Box[A])(f: A ==> B): Box[B] =
+  b[Box[B]]((x: A) => box(f(x)))
+
+def lazymap[A <: Top, B <: Top](b: Box[A])(f: A ==> B): () => Box[B] =//retains b.type | f.type =
+  () => b[Box[B]]((x: A) => box(f(x)))

tests/pos-special/captures/boxmap.scala

@@ -0,0 +1,21 @@
+type Top = Any retains *
+class Cap extends Retains[*]
+
+infix type ==> [A, B] = (A => B) retains *
+
+type Box[+T <: Top] = [K <: Top] => (T ==> K) => K
+
+def box[T <: Top](x: T): Box[T] =
+  [K <: Top] => (k: T ==> K) => k(x)
+
+def map[A <: Top, B <: Top](b: Box[A])(f: A ==> B): Box[B] =
+  b[Box[B]]((x: A) => box(f(x)))
+
+def lazymap[A <: Top, B <: Top](b: Box[A])(f: A ==> B): (() => Box[B]) retains b.type | f.type =
+  () => b[Box[B]]((x: A) => box(f(x)))
+
+def test[A <: Top, B <: Top] =
+  def lazymap[A <: Top, B <: Top](b: Box[A])(f: A ==> B) =
+    () => b[Box[B]]((x: A) => box(f(x)))
+  val x: (b: Box[A]) => (f: A ==> B) => (() => Box[B]) retains b.type | f.type = lazymap[A, B]
+  ()