Error when using `fromString`

Created by: jlongster

Trying to take operators like < and return something like { op: "<" }:

syntax foo = function(ctx) {
  const op = ctx.next().value;
  const x = #`dummy`.get(0);
  return #`{ op: ${x.fromString(op.val())} }`;
}

foo +=;

The above fails with Error: [assertion error]: all tokens must have line info.

Just doing #{ op: null } works as well as #${x.fromString(op.val())} } so it's a weird combination of the two.