0005087: First-class modules and polymorphic comparisons make it possible to compare values of different types

Notes
(0005571) frisch (developer) 2010-06-24 09:46	I agree this is an undesirable property. A clean fix would consist in wrapping packaged modules into a block with a unique id and the same tag as object blocks; we would then have the polymorphic equality coincide with the physical one for packages modules (the physical identity being defined by the packing site), and there would be a clean total ordering as well. The overhead would not be completely negligible for some uses of first-class modules, though. Another, more lightweight solution, would attach a special tag to the runtime representation of structures (even when not packaged as first class values). This way, packing and unpacking would remain no-ops at runtime. The polymorphic comparison function would simply fail on this special tag (in the same way it fails for functional or external values). As a side note, exceptions have exactly the same problem: exception A of int;; let x = A 0;; exception A of float list;; let y = A [];; x = y;; (* true *)

(0006223) frisch (developer) 2011-12-10 19:08	... and GADTs will give a third way to have the generic comparison function compares values of different types. I think there is no easy fix, and the problem is not so bad in practice, so I mark this ticket as "won't fix" for now.

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