diff --git a/examples/translate_rectangle.ml b/examples/translate_rectangle.ml
index cf5b984..4d0bc42 100644
--- a/examples/translate_rectangle.ml
+++ b/examples/translate_rectangle.ml
@@ -3,11 +3,11 @@ open Joy
 let () =
   init ();
   background (255, 255, 255, 255);
-  (* Create rectangle transform *)
+  (* Create rectangle transformation *)
   let r1 = rectangle 200 100 in
   let r2 = translate 100 0 r1 in
 
-  (* Display rectangle transform *)
+  (* Display rectangle transformation *)
   set_color (0, 0, 0);
   show [ r1; r2 ];
   write ~filename:"translate_rectangle.png" ()
diff --git a/lib/joy.ml b/lib/joy.ml
index 1096e11..6c38900 100644
--- a/lib/joy.ml
+++ b/lib/joy.ml
@@ -4,6 +4,8 @@ type 'a point = 'a Shape.point
 type shape = Shape.shape
 type shapes = Shape.shapes
 
+type transformation = Transform.transformation
+
 let point = Shape.point
 let circle = Shape.circle
 let rectangle = Shape.rectangle
diff --git a/lib/joy.mli b/lib/joy.mli
index d612149..d7b39f4 100644
--- a/lib/joy.mli
+++ b/lib/joy.mli
@@ -2,6 +2,8 @@ type 'a point = 'a Shape.point
 type shape = Shape.shape
 type shapes = Shape.shapes
 
+type transformation = Transform.transformation
+
 val point : int -> int -> float point
 val circle : ?c:float point -> int -> shape
 val rectangle : ?c:float point -> int -> int -> shape
@@ -9,11 +11,11 @@ val ellipse : ?c:float point -> int -> int -> shape
 val line : ?a:float point -> float point -> shape
 val polygon : float point list -> shape
 val complex : shapes -> shape
-val rotate : int -> shape -> shape
-val translate : int -> int -> shape -> shape
-val scale : float -> shape -> shape
-val compose : ('a -> 'b) -> ('b -> 'c) -> 'a -> 'c
-val repeat : int -> (shape -> shape) -> shape -> shape
+val rotate : int -> transformation
+val translate : int -> int -> transformation
+val scale : float -> transformation
+val compose : transformation -> transformation -> transformation
+val repeat : int -> transformation -> transformation
 val context : Context.context option ref
 val set_color : int * int * int -> unit
 val background : int * int * int * int -> unit
diff --git a/lib/transform.ml b/lib/transform.ml
index 24831f5..29cd29b 100644
--- a/lib/transform.ml
+++ b/lib/transform.ml
@@ -1,5 +1,7 @@
 open Shape
 
+type transformation = (shape -> shape)
+
 let rec translate dx dy shape =
   match shape with
   | Circle circle ->
diff --git a/lib/transform.mli b/lib/transform.mli
index 4dde434..6fa2fa1 100644
--- a/lib/transform.mli
+++ b/lib/transform.mli
@@ -1,5 +1,7 @@
-val translate : int -> int -> Shape.shape -> Shape.shape
-val scale : float -> Shape.shape -> Shape.shape
-val rotate : int -> Shape.shape -> Shape.shape
-val compose : ('a -> 'b) -> ('b -> 'c) -> 'a -> 'c
-val repeat : int -> (Shape.shape -> Shape.shape) -> Shape.shape -> Shape.shape
+type transformation = (Shape.shape -> Shape.shape)
+
+val translate : int -> int -> transformation
+val scale : float -> transformation
+val rotate : int -> transformation
+val compose : transformation -> transformation -> transformation
+val repeat : int -> transformation -> transformation