Chapel overloaded operator syntax error

channel.chpl

module Channel {

  use semaphore;

  record chan {
    type eltType;
    var size:   int;
    var buffer: [0..size-1] eltType;
    
    var full: semaphore.Semaphore;
    var empty: semaphore.Semaphore;
    var sendX: int = 0;
    var recvX: int = 0;

    var mutex$: sync bool = true;

    proc init(type eltType, size: int){
      this.eltType = eltType;
      this.size = size;
      this.full = new semaphore.Semaphore(0);
      this.empty = new semaphore.Semaphore(size);
    }

    proc send(el:eltType) {
      empty.wait();
      mutex$.readFE();
      buffer[recvX] = el;
      recvX = (recvX + 1) % size;
      mutex$.writeEF(true);
      full.signal();
    }

    proc read() {
      full.wait();
      mutex$.readFE();
      var res:t = buffer[sendX];
      sendX = (sendX + 1) % size;
      mutex$.writeEF(true);
      empty.signal();
      return res;
    }

    proc << (ref val, ref ch:chan){
      val = ch.read();
    }

    proc >> (const val, ref ch:chan){
      ch.write(val);
    }
  }
}

main.chpl

use Channel;

proc worker(ref ch: chan){
  for i in 1..10 do{
    writeln("Will send ", i);
    i >> ch;
  }
}

proc consumer(ref ch: chan){
  for i in 1..10 do
    writeln("read ", ch.read());
}

proc main(){
  var ch = new chan(int, 10);

  coforall i in 1..2 with (ref ch) {  
    if i%2 == 0 then
      consumer(ch);
    else
      worker(ch);
  }
  writeln("Finished!");
}