Postcondition `ensures` does not compile when ref parameter provided about bosquelanguage

[mrkmarron]

Yes, you are right this is a bug and thanks for reporting it.

The problem is in the ensures clause the ref variable should refer to the final value but you might also want to refer to the input value as well. Unfortunately, there was no consistent syntax for this at the time and I just dropped in a TODO placeholder comment.

In my hacking branch I am trying out a $ binder syntax to fix both this bug and the underlying problem. The result should look something like:

function inc(ref x: Int): Bool 
  ensures x =$$ x + 1;
{
  x = x + 1;
  return true;
}