RE: Promotion of bare decorations & comparisons

[Michel Hack <mhack@xxxxxxx>]

Nate wrote (assuming a threshold of at least "dac"):
>    [1,2] \subseteq floor([5,6])
>        = [1,2] \subseteq ([5,6],def) // decorated result
>        = [1,2] \subseteq def         // compress decorated result
>                                         (throw away interval part)
>        = [1,2] \subseteq Entire      // promote def to Entire for comparison
>        = true
>
>That is a false positive, no?

Compressed intervals have to be used carefully, in a context where they
make sense, namely arithmetic expressions.  The promotion rules are there
to complete the picture, but programs have to be written to take these
into account.

> IMO, it is much better to have the bare decoration promote to Empty
> to avoid this situation.

You can construct an equally silly example with that alternative:
     [1,2] \subseteq floor([0,6])
         ...
         = [1,2] \subseteq Empty
         = false

Now we have a false negative.

Michel.
---Sent: 2013-01-03 21:51:12 UTC