bug that exhibits code generation bug

gistfile2.txt

Warning: typeclass IByteStream entry read_line is not virtual
bar/webserver.cpp: In member function ‘void* flxusr::webserver::aux::apply()’:
bar/webserver.cpp:107: error: ‘pc’ was not declared in this scope
compilation terminated due to -Wfatal-errors.

webserver.flx

// -----------------------------------------------------------------------------

union error[E,A] =
  | Error of E
  | Ok of A
;

// -----------------------------------------------------------------------------

include "std/io/faio";
include "std/io/demux";
open Demux;
open Faio;

type socket_t = "int";
type socketio_request = "flx::faio::socketio_request";

gen mk_socketio_request: demuxer * socket_t * address * int * bool -> socketio_request
  = 'flx::faio::socketio_request($1, $2, (char*)$3, $4, $5)';

fun get_pb: socketio_request -> sel_param_ptr = '&$1.sv.pb';

// read & write differ only by a flag
gen async_rw(fd: socket_t, buf: address, var len: int, read_flag: bool) = {
  var eof: bool;
  var asyncb = mk_socketio_request(sys_demux,fd, buf, len, read_flag);
  faio_req$ &asyncb;

  calc_eof(asyncb.pb, &len, &eof);

  return Ok[int,int] len;
}

gen async_read(fd: socket_t, buf: address, len: int) = {
  return async_rw(fd, buf, len, true);      // read
}

// -----------------------------------------------------------------------------

typeclass IByteStream[T] {
  virtual gen read: T * address * int -> error[int,int];

  gen read_line (istream: T) = {
    var c: char;
    val ac = address (&c);
    var st = "";

    gen aux () =>
      match read(istream, ac, 1) with
      | Error ?e => { return Error[int,string] e; }
      | Ok ?len => {
          if len == 0 do
            return Ok[int,string] st;
          else
            return aux ();
          done
        }
      endmatch ()
    ;

    return aux ();
  }
}

// -----------------------------------------------------------------------------

instance IByteStream[socket_t]
{
  gen read(s: socket_t, buf: address, len: int) = {
    return async_read(s, buf, len);
  }
}

open IByteStream[socket_t];

// -----------------------------------------------------------------------------

proc handler (k:socket_t) () {
  match read_line k with
  | Error ?e => { }
  | Ok ?line => { }
  endmatch;
};

var s: socket_t;
spawn_fthread$ handler s;