diff --git a/ocaml/dune-project b/ocaml/dune-project
index 2c6159d..69dc51b 100644
--- a/ocaml/dune-project
+++ b/ocaml/dune-project
@@ -10,9 +10,10 @@
   (description "The compiler for Yanais")
   (depends
     (cmdliner (>= 1.1))
+    (gen (>= 0.5))
     (integers (>= 0.2))
     (menhir (>= 20220210))
-    (uucp (>= 15.0))
+    (sedlex (>= 3.0))
   )
 )
 
diff --git a/ocaml/lib/dune b/ocaml/lib/dune
index 4661737..fea2956 100644
--- a/ocaml/lib/dune
+++ b/ocaml/lib/dune
@@ -2,6 +2,6 @@
   (name yanais_core)
   (public_name yanais.yanais_core)
   (synopsis "The compiler for Yanais")
-  (libraries integers uucp))
+  (libraries integers yanais_parse))
 
 (documentation)
diff --git a/ocaml/lib/syntax.ml b/ocaml/lib/syntax.ml
new file mode 100644
index 0000000..cbd9d21
--- /dev/null
+++ b/ocaml/lib/syntax.ml
@@ -0,0 +1,33 @@
+(* unevaluated expressions with no runtime variables *)
+
+(* de-Bruijn index onto the stack *)
+type stack_ref = int
+
+open Yanais_parse
+
+type pattern =
+  | PatIgnore of Lex.loc_span
+  | PatName of Lex.tagged_ident
+  | PatRecord of pattern record
+
+and pattern_mt = pattern * ((Lex.loc_span * expr) option)
+
+and 'a record = (Lex.loc_span * (string option) * 'a) list
+
+and lambda =
+  { pat       : pattern_mt
+  ; body_span : Lex.loc_span
+  ; body      : expr
+  }
+
+and expr =
+  | Infer
+  | ELiteral of Literal.lit
+  | Use of stack_ref
+  | Lambda of lambda
+  | TyLambda of expr * lambda
+  | Apply of expr * Lex.loc_span * expr
+  | RefOf of expr
+  | RefTy of stack_ref * expr
+  | Record of expr record
+  | TyRecord of expr record
diff --git a/ocaml/libparse/dune b/ocaml/libparse/dune
new file mode 100644
index 0000000..ee94d07
--- /dev/null
+++ b/ocaml/libparse/dune
@@ -0,0 +1,9 @@
+(library
+  (name yanais_parse)
+  (public_name yanais.yanais_parse)
+  (synopsis "Parser for Yanais")
+  (libraries integers sedlex)
+  (preprocess
+    (pps sedlex.ppx)))
+
+(documentation)
diff --git a/ocaml/libparse/lex.ml b/ocaml/libparse/lex.ml
new file mode 100644
index 0000000..7630136
--- /dev/null
+++ b/ocaml/libparse/lex.ml
@@ -0,0 +1,86 @@
+(* A lexer for yanais *)
+
+(* it is not necessary to be able to deal with source files >= 4GiB *)
+type loc_span =
+  { file   : string;
+    start  : int;
+    length : Unsigned.UInt32.t;
+  }
+
+type tagged_ident = TaggedIdent of loc_span * string
+
+type grp_state = Open | Close
+
+type token =
+  | Paren of grp_state
+  | Brace of grp_state
+  | LArr
+  | RArr
+  | LDubArr
+  | RDubArr
+  | Caret
+  | Dot
+  | DubColon
+  | SemiColon
+  | Assign
+  | LLiteral of Literal.lit
+  | Ident of string
+  | PatOut of string
+  | DotIdent of string
+  | Symbol
+
+type token_ann = token * loc_span
+
+type lexer =
+  { buf  : Sedlexing.lexbuf;
+    file : string
+  }
+
+let l_digit = [%sedlex.regexp? '0' .. '9']
+let l_number = [%sedlex.regexp? Plus l_digit]
+let l_ident = [%sedlex.regexp? xid_start, Star xid_continue]
+
+let l_encap lx res = (res,
+  { file = lx.file
+  ; start = Sedlexing.lexeme_start lx.buf
+  ; length = Unsigned.UInt32.of_int (Sedlexing.lexeme_length lx.buf)
+  })
+
+let l_ow_ident lx wrap =
+  let buf = lx.buf in
+  match%sedlex buf with
+  | ("" | l_ident | eof) -> Sedlexing.Utf8.lexeme buf |> wrap |> l_encap lx
+  | _ -> failwith "Unexpected character (internal error)"
+
+let rec tokens lx =
+  let buf = lx.buf in
+  match%sedlex buf with
+    | l_number ->
+      let res = LLiteral (Sedlexing.Utf8.lexeme buf |> fun x -> Literal.LNatural (int_of_string x)) in
+      let res = l_encap lx res in
+      res :: (tokens lx)
+    | l_ident ->
+      let cur = Sedlexing.Utf8.lexeme buf in
+      let res = match Literal.of_str cur with
+        | None -> Ident cur
+        | Some x -> LLiteral x
+      in
+      let res = l_encap lx res in
+      res :: (tokens lx)
+    | '$' ->
+      let res = l_ow_ident lx (fun x -> PatOut x) in
+      res :: (tokens lx)
+    | '.' ->
+      let res = l_ow_ident lx (fun x -> DotIdent x) in
+      res :: (tokens lx)
+    | white_space -> tokens lx
+    | eof -> []
+    | _ -> failwith "Unexpected character"
+
+let run file dat =
+  let lx =
+    { buf = Sedlexing.Utf8.from_gen dat
+    ; file = file
+    } in
+  Sedlexing.set_filename lx.buf file;
+  tokens lx
diff --git a/ocaml/lib/lex.ml b/ocaml/libparse/lex.mli
similarity index 52%
rename from ocaml/lib/lex.ml
rename to ocaml/libparse/lex.mli
index 5316797..b899a21 100644
--- a/ocaml/lib/lex.ml
+++ b/ocaml/libparse/lex.mli
@@ -1,5 +1,13 @@
 (* A lexer for yanais *)
 
+type loc_span = {
+    file   : string;
+    start  : int;
+    length : Unsigned.UInt32.t;
+  }
+
+type tagged_ident = TaggedIdent of loc_span * string
+
 type grp_state = Open | Close
 
 type token =
@@ -14,7 +22,12 @@ type token =
   | DubColon
   | SemiColon
   | Assign
+  | LLiteral of Literal.lit
   | Ident of string
   | PatOut of string
   | DotIdent of string
   | Symbol
+
+type token_ann = token * loc_span
+
+val run : string -> char Gen.t -> token_ann list
diff --git a/ocaml/lib/lit.ml b/ocaml/libparse/literal.ml
similarity index 100%
rename from ocaml/lib/lit.ml
rename to ocaml/libparse/literal.ml
diff --git a/ocaml/lib/lit.mli b/ocaml/libparse/literal.mli
similarity index 100%
rename from ocaml/lib/lit.mli
rename to ocaml/libparse/literal.mli