anchor.diff:  
     src = fetchurl {
       url = "${webpage}/releases/${pname}-${version}.tbz";
  -    sha256 = "0jj5hrqxdb6yyplnz0r7am4mbjzgcn876qp7sqs2x93a97fk6lwd";
  +    sha256 = "181sz6l5xrj5jvwg4m2yqsjzwp2s5h8v0mwhjcwbam90kdfx2nak";
     };
   
     buildInputs = [ ocaml findlib ocamlbuild topkg ];
   
     propagatedBuildInputs = [ uchar result gg ]
                             ++ optionals pdfBackend [ uutf otfm ]
  -                          ++ optionals htmlcBackend [ js_of_ocaml js_of_ocaml-ocamlbuild js_of_ocaml-ppx ];
  +                          ++ optionals htmlcBackend [ js_of_ocaml js_of_ocaml-ppx ];
   
     buildPhase = topkg.buildPhase
       + " --with-uutf ${boolToString pdfBackend}"
  
positive.code:   inherit (stdenv.lib) optionals versionAtLeast;
  
    pname = "vg";
    version = "0.9.3";
    webpage = "https://erratique.ch/software/${pname}";
  in
  
  
negative.code: { stdenv, lib, fetchurl, ocaml, findlib, ocamlbuild, topkg
  , uchar, result, gg, uutf, otfm
  , js_of_ocaml, js_of_ocaml-ppx,
    pdfBackend ? true, # depends on uutf and otfm
    htmlcBackend ? true # depends on js_of_ocaml
  }:
  