Original bug ID: 5668
Reporter: @alainfrisch
Assigned to: @diml
Status: closed (set by @xavierleroy on 2015-12-11T18:07:05Z)
Resolution: fixed
Priority: normal
Severity: minor
Fixed in version: 4.00.0+dev
Category: -for Camlp4 use https://github.com/ocaml/camlp4/issues

Bug description

The following code, taken from pa_js.ml in js_of_ocaml, creates a fragment which produces a syntax error (when Camlp4 prints the AST as source code):

let constr =
  let y = random_var () in
  let body =
    let o = <:expr< $lid:y$ >> in
    let _loc = m_loc in <:expr< ($o$#$m$ : $m_typ$) >>
  in
  <:expr< fun ($lid:y$ : $obj_type$) -> $body$ >>
in
<:expr< let $lid:x$ = $obj$ in
        let _ = $constr$ in
        $f x$ >>

The pre-processed code looks like:

let _ (foo : 'a) = ...

which is not valid OCaml syntax.