Add take-rw, to allow taking of rw containers instead of lvalues.

(The existing C<take> function still also returns lvalues... but
now we can start to correct that.)

src/builtins/control.pir

@@ -221,11 +221,19 @@ on the number of elements.
     throw e
 .end
 
-=item take
+=item take and take-rw
 
 =cut
 
 .sub '&take'
+    .param pmc values :slurpy
+    x_enter_sublog
+    values = '&take-rw'(values :flat)
+    .return (values)
+.end
+
+
+.sub '&take-rw'
     .param pmc values :slurpy
     x_enter_sublog
     .local pmc ex, p6ex

src/core/Any-list.pm

@@ -59,7 +59,7 @@ augment class Any {
     our multi method grep(Mu $test) is rw {
         gather {
             for @.list {
-                take $_ if $_ ~~ $test;
+                take-rw $_ if $_ ~~ $test;
             }
         }
     }
@@ -273,7 +273,7 @@ augment class Any {
         gather for $.list -> $value {
             my $key = $i++;
             take $key;
-            take $value;
+            take-rw $value;
         }
     }
 
@@ -287,7 +287,7 @@ augment class Any {
 
     multi method values() is rw {
         gather for $.list -> $value {
-            take $value;
+            take-rw $value;
         }
     }