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Robert Virding <robert.virding@erlang-solutions.com> writes:
> I personally think that having things undefined, implementation
> specific, and still not illegal is a Bad Thing (tm).
...
> No, it is worth converting undefined to error generating illegal.

Such a guarantee comes with a cost, which can sometimes be very high;
detecting violations can be quite hard / expensive, or even
impossible.

In some cases the cost is clearly worth it -- mistakes which are very
easy for a user to make, and easy to detect -- but in others, it is
not: for instance, situations which are costly to detect and only
result from obviously silly or extremely unlikely user code.

Obviously there's lots of stuff "in the middle" which needs a
judgement call, and given Lua's target market, I think the Lua devs
have done a pretty reasonable job of that.

-miles

-- 
「寒いね」と話しかければ「寒いね」と答える人のいるあったかさ [俵万智]