What happens when a user creates a record with immutable fields and then calls (rtd-contructor rtd fieldspecs) without those fields specified? or if the field is shadowed, what would the value of that field be? Seems that there would have to be a way to define the default value of an immutable field. I think the best approach is to abandon this version of the function since the underlying reason only applied to mutable fields. I'm not sure what this feature provides that the user can't accomplish themselves by closing over the constructor function. Also, there should be an acknowledgment link to Pavel Curtis' actual proposal.