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diff --git a/users/wpcarro/scratch/compiler/expr_parser.ml b/users/wpcarro/scratch/compiler/expr_parser.ml
new file mode 100644
index 0000000000..797592931a
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+++ b/users/wpcarro/scratch/compiler/expr_parser.ml
@@ -0,0 +1,187 @@
+(*******************************************************************************
+ * CLI REPL for an s-expression Lambda Calculus.
+ *
+ * Lambda Calculus Expression Language:
+ *
+ *   Helpers:
+ *     symbol     -> [-a-z]+
+ *     string     -> '"' [^"]* '"'
+ *     boolean    -> 'true' | 'false'
+ *     integer    -> [1-9][0-9]*
+ *
+ *   Core:
+ *     expression -> funcdef
+ *     binding    -> '(' 'let' symbol expr expr ')'
+ *     funcdef    -> '(' 'fn' symbol expr ')'
+ *     funccall   -> '(' ( symbol | funcdef) expr ')'
+ *     literal    -> string | boolean | integer
+ *     variable   -> symbol
+ *
+ * Example Usage:
+ *   $ ocamlopt types.ml str.cmxa inference.ml parser.ml expr_parser.ml && ./a.out
+ *   repl> true
+ *   tokens: [ "true" ]
+ *   ast: ValueLiteral (LiteralBool true)
+ *   Boolean
+ *   repl>
+ *
+ ******************************************************************************)
+
+open Parser
+open Inference
+open Debug
+open Prettify
+open Vec
+
+type literal = LiteralBool of bool | LiteralInt of int
+
+let ( let* ) = Option.bind
+let map = Option.map
+
+let tokenize (x : string) : token vec =
+  let xs = Vec.create () in
+  let i = ref 0 in
+  while !i < String.length x do
+    match x.[!i] with
+    | ' ' -> i := !i + 1
+    (* strings *)
+    | '"' ->
+      let curr = ref "\"" in 
+      i := !i + 1;
+      while x.[!i] != '"' do
+        curr := !curr ^ "?";
+        i := !i + 1
+      done;
+      curr := !curr ^ "\"";
+      Vec.append !curr xs;
+      i := !i + 1
+    | '(' ->
+        Vec.append "(" xs;
+        i := !i + 1
+    | ')' ->
+        Vec.append ")" xs;
+        i := !i + 1
+    | _ ->
+        let token = ref "" in
+        while !i < String.length x && not (String.contains "() " x.[!i]) do
+          token := !token ^ String.make 1 x.[!i];
+          i := !i + 1
+        done;
+        Vec.append !token xs
+  done;
+  xs
+
+let parse_symbol (p : parser) : string option =
+  let* x = p#curr in
+  if Str.string_match (Str.regexp "[-a-z][0-9]*") x 0 then
+    begin
+      p#advance;
+      Some x
+    end
+  else
+    None
+
+let parse_variable (p : parser) : Types.value option =
+  let* x = parse_symbol p in
+  Some (Types.ValueVariable x)
+
+let parse_literal (p : parser) : Types.value option =
+  match p#curr with
+  | Some "true" ->
+     p#advance;
+     Some (ValueLiteral (LiteralBool true))
+  | Some "false" ->
+     p#advance;
+     Some (ValueLiteral (LiteralBool false))
+  | Some x ->
+     (match int_of_string_opt x with
+      | Some n ->
+         p#advance;
+         Some (ValueLiteral (LiteralInt n))
+      | _ -> 
+        if String.starts_with ~prefix:"\"" x then
+          begin
+            p#advance;
+            Some (ValueLiteral (LiteralString x))
+          end
+        else
+          parse_variable p)
+  | _ -> None
+
+let rec parse_expression (p : parser) : Types.value option =
+  parse_binding p
+
+and parse_funccall (p : parser) : Types.value option =
+  match (p#curr, p#next) with
+  | (Some "(", Some "(") ->
+     p#advance;
+     let* f = parse_funcdef p in
+     let* x = parse_expression p in
+     p#expect ")";
+     Some (Types.ValueApplication (f, x))
+  | (Some "(", _) ->
+     p#advance;
+     let* f = parse_symbol p in
+     let* x = parse_expression p in
+     p#expect ")";
+     Some (Types.ValueVarApplication (f, x))
+  | _ -> parse_literal p
+
+and parse_funcdef (p : parser) : Types.value option =
+  match (p#curr, p#next) with
+  | (Some "(", Some "fn") ->
+     p#advance;
+     p#advance;
+     let* name = parse_symbol p in
+     let* body = parse_expression p in
+     p#expect ")";
+     Some (Types.ValueFunction (name, body))
+  | _ -> parse_funccall p
+
+and parse_binding (p : parser) : Types.value option =
+  match (p#curr, p#next) with
+  | (Some "(", Some "let") ->
+     p#advance;
+     p#advance;
+     let* name = parse_symbol p in
+     let* value = parse_expression p in
+     let* body = parse_expression p in
+     Some (Types.ValueBinder (name, value, body))
+  | _ -> parse_funcdef p
+
+let print_tokens (xs : string vec) : unit =
+  xs 
+  |> Vec.map (Printf.sprintf "\"%s\"")
+  |> Vec.join ", "
+  |> Printf.sprintf "tokens: [ %s ]"
+  |> print_string 
+  |> print_newline
+
+let parse_language (x : string) : Types.value option =
+  let tokens = tokenize x in
+  print_tokens tokens;
+  parse_expression (new parser tokens)
+
+let main =
+  while true do
+    begin
+      print_string "repl> ";
+      let x = read_line () in
+      match parse_language x with
+      | Some ast ->
+         (match ast |> Debug.print Debug.ast "ast" |> do_infer with
+          | None ->
+             "Type-check failed"
+             |> print_string
+             |> print_newline
+          | Some x ->
+             x
+             |> Prettify.type'
+             |> print_string
+             |> print_newline)
+      | None ->
+         "Could not parse"
+         |> print_string
+         |> print_newline
+    end
+  done