gistfile1.txt

diff --git a/src/core/Set.pm b/src/core/Set.pm
index c7e8afe..20b887e 100644
--- a/src/core/Set.pm
+++ b/src/core/Set.pm
@@ -16,7 +16,7 @@ my class Set is Iterable does Associative {
         my %e;
         sub register-arg($arg) {
             given $arg {
-                when Pair { %e{.key} = True; }
+                when Pair { if .value { %e{.key} = True; } }
                 when Set | KeySet { for .keys -> $key { %e{$key} = True; } }
                 when Associative { for .pairs -> $p { register-arg($p); } }
                 when Positional { for .list -> $p { register-arg($p); } }
@@ -60,7 +60,7 @@ sub set(*@args) {
     Set.new(@args);
 }
 
-my class KeySet is Iterable does Associative {
+my class KeyHash is Iterable does Associative {
     has %!elems;
 
     method keys { %!elems.keys }
@@ -82,7 +82,7 @@ my class KeySet is Iterable does Associative {
         my %e;
         sub register-arg($arg) {
             given $arg {
-                when Pair { %e{.key} = True; }
+                when Pair { if .value { %e{.key} = True; } }
                 when Set | KeySet { for .keys -> $key { %e{$key} = True; } }
                 when Associative { for .pairs -> $p { register-arg($p); } }
                 when Positional { for .list -> $p { register-arg($p); } }
@@ -107,3 +107,6 @@ my class KeySet is Iterable does Associative {
     method pick($count = 1) { %!elems.keys.pick($count) }
     method roll($count = 1) { %!elems.keys.roll($count) }
 }
+
+my class KeySet    is KeyHash { } # XXX Should be KeyHash of Bool
+my class KeyWeight is KeyHash { } # XXX Should be KeyHash of Rat