diff --git a/testing/btest/Baseline/language.closure-sending/recv.recv.out b/testing/btest/Baseline/language.closure-sending/recv.recv.out
index 4760591c3c..d48a41b96d 100644
--- a/testing/btest/Baseline/language.closure-sending/recv.recv.out
+++ b/testing/btest/Baseline/language.closure-sending/recv.recv.out
@@ -2,26 +2,26 @@
 hello :-)
 peer added
 receiver got ping: function 2
-inside: 1 | outside: 11 | global: 100
+inside: 1 | outside: 12 | global: 100
 77
 receiver got ping: function 1
 begin: 100 | base_step: 2
 begin: 100 | base_step: 2 | step: 76
 178
 receiver got ping: function 2
-inside: 3 | outside: 11 | global: 100
+inside: 3 | outside: 12 | global: 100
 79
 receiver got ping: function 1
 begin: 100 | base_step: 4
 begin: 100 | base_step: 4 | step: 76
 180
 receiver got ping: function 2
-inside: 5 | outside: 11 | global: 100
+inside: 5 | outside: 12 | global: 100
 81
 receiver got ping: function 1
 begin: 100 | base_step: 6
 begin: 100 | base_step: 6 | step: 76
 182
 receiver got ping: function 2
-inside: 7 | outside: 11 | global: 100
+inside: 7 | outside: 12 | global: 100
 83
diff --git a/testing/btest/Baseline/language.closure-sending/send.send.out b/testing/btest/Baseline/language.closure-sending/send.send.out
index 11c6f46d91..39d70d48d5 100644
--- a/testing/btest/Baseline/language.closure-sending/send.send.out
+++ b/testing/btest/Baseline/language.closure-sending/send.send.out
@@ -3,7 +3,7 @@ hello :)
 peer added
 begin: 100 | base_step: 50
 sender got pong: function 2
-inside: 1 | outside: 11 | global: 10
+inside: 1 | outside: 12 | global: 10
 77
 begin: 100 | base_step: 50
 sender got pong: function 1
@@ -12,7 +12,7 @@ begin: 178 | base_step: 2 | step: 76
 256
 begin: 100 | base_step: 50
 sender got pong: function 2
-inside: 3 | outside: 11 | global: 10
+inside: 3 | outside: 12 | global: 10
 79
 begin: 100 | base_step: 50
 sender got pong: function 1
@@ -21,7 +21,7 @@ begin: 180 | base_step: 4 | step: 76
 260
 begin: 100 | base_step: 50
 sender got pong: function 2
-inside: 5 | outside: 11 | global: 10
+inside: 5 | outside: 12 | global: 10
 81
 begin: 100 | base_step: 50
 sender got pong: function 1
diff --git a/testing/btest/Baseline/language.function-closures/out b/testing/btest/Baseline/language.function-closures/out
index 648170033b..13869d6338 100644
--- a/testing/btest/Baseline/language.function-closures/out
+++ b/testing/btest/Baseline/language.function-closures/out
@@ -19,8 +19,8 @@ expect: 160
 160
 expect: 225
 225
-expect: 290
-290
+expect: 225
+225
 
 tables:
 
diff --git a/testing/btest/Baseline/language.hook_calls/invalid.out b/testing/btest/Baseline/language.hook_calls/invalid.out
index 2ce20fc128..762168bcef 100644
--- a/testing/btest/Baseline/language.hook_calls/invalid.out
+++ b/testing/btest/Baseline/language.hook_calls/invalid.out
@@ -1,11 +1,9 @@
 ### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
 error in ./invalid.zeek, line 9: hook cannot be called directly, use hook operator (myhook)
-warning in ./invalid.zeek, line 9: expression value ignored (myhook(3))
 error in ./invalid.zeek, line 10: hook cannot be called directly, use hook operator (myhook)
 error in ./invalid.zeek, line 11: hook cannot be called directly, use hook operator (myhook)
 error in ./invalid.zeek, line 12: not a valid hook call expression (2 + 2)
 warning in ./invalid.zeek, line 12: expression value ignored (2 + 2)
 error in ./invalid.zeek, line 13: not a valid hook call expression (2 + 2)
 error in ./invalid.zeek, line 15: hook cannot be called directly, use hook operator (h)
-warning in ./invalid.zeek, line 15: expression value ignored (h(3))
 error in ./invalid.zeek, line 16: hook cannot be called directly, use hook operator (h)
diff --git a/testing/btest/language/closure-sending-naming.zeek b/testing/btest/language/closure-sending-naming.zeek
index 4210c758cb..27bc367d6d 100644
--- a/testing/btest/language/closure-sending-naming.zeek
+++ b/testing/btest/language/closure-sending-naming.zeek
@@ -33,7 +33,7 @@ function send_event()
     local log : myfunctype = function(c: count) : function(d: count) : count
         {
         # print fmt("inside: %s | outside: %s | global: %s", c, event_count, global_with_same_name);
-        return function(d: count) : count { return d + c; };
+        return function[c](d: count) : count { return d + c; };
         };
 
         local e2 = Broker::make_event(ping, "function 1", log);
@@ -85,7 +85,7 @@ function my_funcs()
     local l : myfunctype = function(c: count) : function(d: count) : count
     {
     print fmt("dogs");
-    return function(d: count) : count { return d + c; };
+    return function[c](d: count) : count { return d + c; };
     };
     }
 
diff --git a/testing/btest/language/closure-sending.zeek b/testing/btest/language/closure-sending.zeek
index c6ff25464c..f5a3e44035 100644
--- a/testing/btest/language/closure-sending.zeek
+++ b/testing/btest/language/closure-sending.zeek
@@ -54,6 +54,7 @@ function send_event()
 	local stepper = l(50);
 
     ++n;
+    ++event_count;
     if ( n % 2 == 0)
         {
         local e2 = Broker::make_event(ping, "function 1", l);
diff --git a/testing/btest/language/function-closures.zeek b/testing/btest/language/function-closures.zeek
index 80112da0cf..c4e4505481 100644
--- a/testing/btest/language/function-closures.zeek
+++ b/testing/btest/language/function-closures.zeek
@@ -3,9 +3,11 @@
 
 global numberone : count = 1;
 
+type mutable_aggregate: record { x: count; };
+
 function make_count_upper (start : count) : function(step : count) : count
 	{
-	return function(step : count) : count
+	return function[start](step : count) : count
 		{ return (start += (step + numberone)); };
         }
 
@@ -14,7 +16,7 @@ function dog_maker(name: string, weight: count) : function (action: string)
 	local eat = function (lbs: count) { print fmt("eat i weigh %s", lbs); };
 	local bark = function (who: string) { print fmt("bark i am %s", who); };
 
-	local dog = function (action: string)
+	local dog = function [eat, bark, name, weight](action: string)
 		{
 		switch action
 			{
@@ -72,14 +74,14 @@ event zeek_init()
 	print c(1) == two(3);
 	
 	# a little more complicated ...
-	local cat_dog = 100;
-	local add_n_and_m = function(n: count) : function(m : count) : function(o : count) : count
+	local cat_dog = mutable_aggregate($x=100);
+	local add_n_and_m = function[cat_dog](n: count) : function(m : count) : function(o : count) : count
 		{
-		cat_dog += 1;
+		cat_dog$x += 1;
 		local can_we_make_variables_inside = 11;
-		return function(m : count) : function(o : count) : count
-			{ return function(o : count) : count
-				{ return  n + m + o + cat_dog + can_we_make_variables_inside; }; };
+		return function[can_we_make_variables_inside, cat_dog, n](m : count) : function(o : count) : count
+			{ return function[cat_dog, can_we_make_variables_inside, m, n](o : count) : count
+				{ return  n + m + o + cat_dog$x + can_we_make_variables_inside; }; };
 		};
 
 	local add_m = add_n_and_m(2);
@@ -95,14 +97,14 @@ event zeek_init()
 
 	# can mutate closure:
 	print "expect: 101";
-	print cat_dog;
+	print cat_dog$x;
 	
 	# complicated - has state across calls
 	local two_part_adder_maker = function (begin : count) : function (base_step : count) : function ( step : count) : count
 		{
-		return function (base_step : count) : function (step : count) : count
+		return function [begin](base_step : count) : function (step : count) : count
 			{
-				return function (step : count) : count
+				return function [base_step, begin](step : count) : count
 					{
 					return (begin += base_step + step); }; }; };
 	
@@ -115,10 +117,17 @@ event zeek_init()
 	print stepper(15);
 
 	# another copy check
-	print "expect: 290";
+	#
+	# under old reference capture semantics, this would print 290 because
+	# the twotwofive copy wouldn't have a copy of the "begin" variable but
+	# instead a reference to it; under copy capture semantics, though,
+	# those are separate values, so executing stepper() after the copy
+	# won't affect the copy
+	#
+	print "expect: 225";
 	print twotwofive(15);
 
-	local hamster : count = 3;
+	local hamster = mutable_aggregate($x=3);
 	
 	print "";
 	print "tables:";
@@ -128,10 +137,10 @@ event zeek_init()
 	    [1] = "symmetric active",
 	    [2] = "symmetric passive",
 	    [3] = "client",
-            } &default = function(i: count):string { return fmt("unknown-%d. outside-%d", i, hamster += 1); } &redef;
+            } &default = function[hamster](i: count):string { return fmt("unknown-%d. outside-%d", i, hamster$x += 1); } &redef;
 
 	# changing the value here will show in the function.
-	hamster += hamster;
+	hamster$x += hamster$x;
 	
 	print "expect: unknown-11. outside-7";
 	print modes[11];
@@ -156,7 +165,7 @@ event zeek_init()
             [1] = "symmetric active",
             [2] = "symmetric passive",
             [3] = "client"
-	)&default = function(i: count):string { return fmt("unknown-%d. outside-%d", i, hamster_also += 1); } &redef;
+	)&default = function[hamster_also](i: count):string { return fmt("unknown-%d. outside-%d", i, hamster_also += 1); } &redef;
 
         print "expect: unknown-11. outside-4";
         print modes_also[11];
diff --git a/testing/btest/language/lambda-escaping.zeek b/testing/btest/language/lambda-escaping.zeek
index 7552d39cb2..8e2deb1af6 100644
--- a/testing/btest/language/lambda-escaping.zeek
+++ b/testing/btest/language/lambda-escaping.zeek
@@ -13,7 +13,7 @@ event zeek_init() &priority=+10
 	{
 	local outer = 101;
 
-	local lambda = function()
+	local lambda = function[outer]()
 		{ print outer; };
 
 	lambda();
diff --git a/testing/btest/language/lambda-nested-copy.zeek b/testing/btest/language/lambda-nested-copy.zeek
index 6cf0e6952a..ae4578fdcd 100644
--- a/testing/btest/language/lambda-nested-copy.zeek
+++ b/testing/btest/language/lambda-nested-copy.zeek
@@ -3,9 +3,9 @@
 
 local outer = 100;
 
-local lambda = function()
+local lambda = function[outer]()
 	{
-	local inner = function(a: count, b: count, c: count, d: count, e: count, f: count)
+	local inner = function[outer](a: count, b: count, c: count, d: count, e: count, f: count)
 		{
 		print outer + f;
 		};
diff --git a/testing/btest/language/lambda-record-field.zeek b/testing/btest/language/lambda-record-field.zeek
index bcb7e1bc75..fb63dbaab8 100644
--- a/testing/btest/language/lambda-record-field.zeek
+++ b/testing/btest/language/lambda-record-field.zeek
@@ -8,6 +8,6 @@ type myrec: record {
 event zeek_init()
 	{
 	local w = "world";
-	local mr = myrec($foo(a: string) = { print a + w; });
+	local mr = myrec($foo[w](a: string) = { print a + w; });
 	mr$foo("hello");
 	}
diff --git a/testing/btest/language/lambda-zeek-init.zeek b/testing/btest/language/lambda-zeek-init.zeek
index 2576831c22..cc596b431b 100644
--- a/testing/btest/language/lambda-zeek-init.zeek
+++ b/testing/btest/language/lambda-zeek-init.zeek
@@ -5,7 +5,7 @@ event zeek_init() &priority=+10
 	{
 	local outer = 101;
 
-	local lambda = function()
+	local lambda = function[outer]()
 		{ print outer + 2; };
 
 	lambda();
diff --git a/testing/btest/language/more-closure-tests.zeek b/testing/btest/language/more-closure-tests.zeek
index f8a01cd0a8..2f6d6fbd91 100644
--- a/testing/btest/language/more-closure-tests.zeek
+++ b/testing/btest/language/more-closure-tests.zeek
@@ -17,7 +17,7 @@ function map_1 (f: function(a: count): count, v: vector of count) : vector of co
 # stacks two functions
 function stacker (one : function(a: count): count, two: function (b: count): count): function(c: count): count
     {
-    return function (c: count): count
+    return function [one,two](c: count): count
         {
         return one(two(c));
         };
@@ -25,7 +25,7 @@ function stacker (one : function(a: count): count, two: function (b: count): cou
 
 function make_dog(name: string, weight: count) : function(i: string, item: string)
     {
-    return function(i: string, item: string)
+    return function[name, weight](i: string, item: string)
         {
         switch i
             {
@@ -69,7 +69,7 @@ event zeek_init()
 
     local make_laster = function(start: count) : function(i: count): count
         {
-        return function(i: count): count
+        return function[start](i: count): count
             {
             local temp = i;
             i += start;
@@ -111,7 +111,7 @@ event zeek_init()
     local vs = vector("dog", "cat", "fish");
     for (i in vs)
         {
-        mfs += function() { print i, vs[i]; };
+        mfs += function[i, vs]() { print i, vs[i]; };
         }
     for ( i in mfs)
         mfs[i]();
diff --git a/testing/btest/language/outer_param_binding.zeek b/testing/btest/language/outer_param_binding.zeek
index 1f3f32a1fc..f3a4686f24 100644
--- a/testing/btest/language/outer_param_binding.zeek
+++ b/testing/btest/language/outer_param_binding.zeek
@@ -9,7 +9,7 @@ function bar(b: string, c: string)
 	{
 	local f: Foo;
 	local d = 8;
-	f = [$x=function(a: string) : string
+	f = [$x=function[b, c, d](a: string) : string
 			{
 			local x = 0;
 			# Fail here: we've captured the closure.