Preserve class when subsetting a list

Author: d-torrance

M2/Macaulay2/m2/lists.m2

@@ -33,7 +33,9 @@ List /  RingElement := List /  Number := List => (v,b) -> apply(v,x->x /  b)
 List // RingElement := List // Number := List => (v,b) -> apply(v,x->x // b)
 List  % RingElement := List  % Number := List => (v,b) -> apply(v,x->x  % b)
 
-VisibleList _ List := VisibleList => (x,y) -> apply(splice y, i -> x#i)
+VisibleList _ List := VisibleList => (x,y) -> (
+    L := class x;
+    new L from apply(splice y, i -> x#i))
 
 Sequence .. Sequence := Sequence => (v,w) -> (
      n := #v;

M2/Macaulay2/packages/Macaulay2Doc/operators/underscore.m2

@@ -47,7 +47,7 @@ document {
      SeeAlso => {(symbol #, BasicList, ZZ)},
      }
 document {
-     Key => (symbol _, VisibleList, List),
+     Key => (symbol _, VisibleList, VisibleList),
      Headline => "get some entries of a list",
      Usage => "w_{i,j,...}",
      Inputs => {

M2/Macaulay2/tests/normal/lists.m2

@@ -18,5 +18,6 @@ assert (net i == "<|x, y, z|>"^0)
 assert (toList i === {x,y,z})
 assert (class i === AngleBarList)
 assert (delete(y, i) == <| x, z |>)
+assert (i_{0,2} == <| x, z |>)
 
 assert isTable table(0, 0, identity)