diff --git a/prelude.ld b/prelude.ld
index b15e3d5..8230825 100644
--- a/prelude.ld
+++ b/prelude.ld
@@ -55,6 +55,26 @@ fn assoc? {
 	(_) -> false
 }
 
+&&& nil: working with nothing
+
+fn nil? {
+	"Returns true if a value is nil."
+	(nil) -> true
+	(_) -> false
+}
+
+fn some? {
+	"Returns true if a value is not nil."
+	(nil) -> false
+	(_) -> true
+}
+
+fn some {
+	"Takes a possibly nil value and a default value. Returns the value if it's not nil, returns the default if it's nil."
+	(nil, default) -> default
+	(value, _) -> value 
+}
+
 & ...and if two things are the same
 fn eq? {
 	"Returns true if all arguments have the same value."
@@ -244,6 +264,13 @@ fn append {
 	(xs as :set, x) -> base :conj (xs, x)
 }
 
+fn append! {
+	"Adds an element to a list, modifying it."
+	() -> []
+	(xs as :list) -> xs
+	(xs as :list, x) -> base :conj! (xs, x)
+}
+
 fn concat {
 	"Combines two lists, strings, or sets."
 	(x as :string, y as :string) -> base :concat (x, y)
@@ -684,27 +711,6 @@ fn keyword? {
 
 & TODO: determine if Ludus should have a `keyword` function that takes a string and returns a keyword. Too many panics, it has weird memory consequences, etc.
 
-&&& nil: working with nothing
-
-fn nil? {
-	"Returns true if a value is nil."
-	(nil) -> true
-	(_) -> false
-}
-
-fn some? {
-	"Returns true if a value is not nil."
-	(nil) -> false
-	(_) -> true
-}
-
-fn some {
-	"Takes a possibly nil value and a default value. Returns the value if it's not nil, returns the default if it's nil."
-	(nil, default) -> default
-	(value, _) -> value 
-}
-
-
 & TODO: make `and` and `or` special forms which lazily evaluate arguments
 fn and {
 	"Returns true if all values passed in are truthy. Note that this does not short-circuit: all arguments are evaulated before they are passed in."
@@ -1094,13 +1100,13 @@ box p5_calls = []
 & it must be the first call to p5.
 box bgcolor = colors :black
 
-fn add_call! (call) -> update! (p5_calls, append (_, call))
+fn add_call! (call) -> update! (p5_calls, append! (_, call))
 
 fn add_command! (command) -> {
-	update! (turtle_commands, append (_, command))	
+	update! (turtle_commands, append! (_, command))
 	let prev = do turtle_states > unbox > last
 	let curr = apply_command (prev, command)
-	update! (turtle_states, append (_, curr))
+	update! (turtle_states, append! (_, curr))
 	let call = state/call ()
 	if call then { add_call! (call); :ok } else :ok
 }
@@ -1323,7 +1329,7 @@ fn turtle_state {
 fn load_turtle_state! {
 	"Sets the turtle state to a previously saved state. Returns the state."
 	(state) -> {
-		update! (turtle_states, append (_, state))
+		update! (turtle_states, append! (_, state))
 		let call = state/call ()
 		if call then { add_call! (call); :ok } else :ok
 	}
diff --git a/src/ludus.janet b/src/ludus.janet
index b438c35..c81a54f 100644
--- a/src/ludus.janet
+++ b/src/ludus.janet
@@ -47,22 +47,33 @@
   (set post (i/interpret prelude/post/ast ctx))
   ([err] (e/runtime-error err)))
  (set (out :draw) (post :draw))
- (-> out j/encode string))
+ out
+ # (-> out j/encode string)
+ )
 
 (comment
 # (do
+ (def start (os/clock))
  (def source `
- add (1, 2)
+repeat 100 {
+ repeat 100 {
+  fd! (1)
+  rt! (inv (100))
+ }
+ rt! (inv (100))
+}
  `)
  (def out (-> source 
   ludus
-  j/decode
+  # j/decode
   ))
+ (def end (os/clock))
  (setdyn :out stdout)
- # (pp out)
- (def console (out "console"))
- (print console)
- (def result (out "result"))
- (print result)
+ (pp out)
+ # (def console (out "console"))
+ # (print console)
+ # (def result (out "result"))
+ # (print result)
+ (print (- end start))
 )