diff --git a/src/haz3lformatter/Formatter.re b/src/haz3lformatter/Formatter.re
new file mode 100644
index 000000000..a60c4a693
--- /dev/null
+++ b/src/haz3lformatter/Formatter.re
@@ -0,0 +1,11 @@
+open Haz3lcore;
+let format = (~inline: bool, s: string): string => {
+  let seg =
+    ExpToSegment.exp_to_segment(
+      ~settings=ExpToSegment.Settings.of_core(~inline, CoreSettings.on),
+      MakeTerm.from_zip_for_sem(Option.get(Printer.zipper_of_string(s))).
+        term,
+    );
+  let zipper = Zipper.unzip(seg);
+  Printer.zipper_to_string(~holes=Some("?"), zipper);
+};
diff --git a/src/haz3lformatter/FormatterMain.re b/src/haz3lformatter/FormatterMain.re
new file mode 100644
index 000000000..726084b4e
--- /dev/null
+++ b/src/haz3lformatter/FormatterMain.re
@@ -0,0 +1,3 @@
+open Haz3lformatter;
+
+print_endline(Formatter.format(~inline=false, In_channel.input_all(stdin)));
diff --git a/test/Test_Formatter.re b/test/Test_Formatter.re
new file mode 100644
index 000000000..86e697e3b
--- /dev/null
+++ b/test/Test_Formatter.re
@@ -0,0 +1,27 @@
+
+open Alcotest;
+open Haz3lcore;
+open Haz3lformatter;
+
+let parse_exp = (s: string) =>
+  MakeTerm.from_zip_for_sem(Option.get(Printer.zipper_of_string(s))).term;
+let serialize = (exp: Exp.t): string => {
+  let seg =
+    ExpToSegment.exp_to_segment(
+      ~settings=ExpToSegment.Settings.of_core(~inline=true, CoreSettings.on),
+      exp,
+    );
+  let zipper = Zipper.unzip(seg);
+  Printer.zipper_to_string(~holes=Some("?"), zipper);
+};
+
+let tests = [
+  test_case("Incomplete Function Definition", `Quick, () => {
+    check(
+      string,
+      "let    = fun x ->   in  ",
+      "let ? = (fun x -> ?) in ?",
+      Formatter.format(~inline=true, "let    = fun x ->   in  "),
+    )
+  }),
+];
diff --git a/test/haz3ltest.re b/test/haz3ltest.re
index 9eed7a992..dea6b375e 100644
--- a/test/haz3ltest.re
+++ b/test/haz3ltest.re
@@ -10,6 +10,7 @@ let (suite, _) =
       ("Evaluator", Test_Evaluator.tests),
       ("MakeTerm", Test_MakeTerm.tests),
       ("ExpToSegment", Test_ExpToSegment.tests),
+      ("Formatter", Test_Formatter.tests),
     ],
   );
 Junit.to_file(Junit.make([suite]), "junit_tests.xml");