diff --git a/src/prettify/PrettyCommon.ml b/src/prettify/PrettyCommon.ml
new file mode 100644
index 0000000..8493fdf
--- /dev/null
+++ b/src/prettify/PrettyCommon.ml
@@ -0,0 +1,35 @@
+module  S = Tail
+
+let rec fmt_list disp fmt xs = match xs with
+| [] -> ()
+| x :: [] -> Format.fprintf fmt "(%a)" disp x
+| x :: xs -> Format.fprintf fmt "(%a) %a" disp x (fmt_list disp) xs
+
+let fmt_var fmt var =
+    Format.fprintf fmt "%s" (Atom.hint var)
+
+let fmt_vars = fmt_list fmt_var
+
+let fmt_op fmt (op: S.binop) =
+    Format.fprintf fmt (
+        match op with
+        | S.OpAdd -> "+"
+        | S.OpSub -> "-"
+        | S.OpMul -> "*"
+        | S.OpDiv -> "/"
+    )
+
+let rec fmt_val fmt (v: S.value) = match v with
+| S.VVar var -> fmt_var fmt var
+| S.VLit intVal -> Format.fprintf fmt "%d" intVal
+| S.VBinOp (v1, op, v2) ->
+        Format.fprintf fmt "%a %a %a"
+            fmt_val v1
+            fmt_op op
+            fmt_val v2
+
+let fmt_vals = fmt_list fmt_val
+
+let fmt_self fmt self = match self with
+| S.NoSelf -> ()
+| S.Self(v) -> Format.fprintf fmt "[%a]" fmt_var v
diff --git a/src/prettify/PrettyCommon.mli b/src/prettify/PrettyCommon.mli
new file mode 100644
index 0000000..70674b1
--- /dev/null
+++ b/src/prettify/PrettyCommon.mli
@@ -0,0 +1,12 @@
+val fmt_list:
+    (Format.formatter -> 'a -> unit) -> Format.formatter -> 'a list -> unit
+
+val fmt_var: Format.formatter -> Atom.atom -> unit
+val fmt_vars: Format.formatter -> Atom.atom list -> unit
+
+val fmt_op: Format.formatter -> Tail.binop -> unit
+
+val fmt_val: Format.formatter -> Tail.value -> unit
+val fmt_vals: Format.formatter -> Tail.value list -> unit
+
+val fmt_self: Format.formatter -> Tail.self -> unit
diff --git a/src/prettify/PrettyTail.ml b/src/prettify/PrettyTail.ml
index cacdb95..dc59fcd 100644
--- a/src/prettify/PrettyTail.ml
+++ b/src/prettify/PrettyTail.ml
@@ -1,38 +1,6 @@
 module  S = Tail
 
-let rec fmt_list disp fmt xs = match xs with
-| [] -> ()
-| x :: [] -> Format.fprintf fmt "(%a)" disp x
-| x :: xs -> Format.fprintf fmt "(%a) %a" disp x (fmt_list disp) xs
-
-let fmt_var fmt var =
-    Format.fprintf fmt "%s" (Atom.hint var)
-
-let fmt_vars = fmt_list fmt_var
-
-let fmt_op fmt (op: S.binop) =
-    Format.fprintf fmt (
-        match op with
-        | S.OpAdd -> "+"
-        | S.OpSub -> "-"
-        | S.OpMul -> "*"
-        | S.OpDiv -> "/"
-    )
-
-let rec fmt_val fmt (v: S.value) = match v with
-| S.VVar var -> fmt_var fmt var
-| S.VLit intVal -> Format.fprintf fmt "%d" intVal
-| S.VBinOp (v1, op, v2) ->
-        Format.fprintf fmt "%a %a %a"
-            fmt_val v1
-            fmt_op op
-            fmt_val v2
-
-let fmt_vals = fmt_list fmt_val
-
-let fmt_self fmt self = match self with
-| S.NoSelf -> ()
-| S.Self(v) -> Format.fprintf fmt "[%a]" fmt_var v
+open PrettyCommon
 
 let rec fmt_block fmt (S.Lam (self, vars, body)) =
     Format.fprintf fmt "λ%a(%a) ·@ %a"