[isabelle-dev] [OT] Checked "assume" command
makarius at sketis.net
Wed Sep 5 15:35:26 CEST 2012
On Wed, 5 Sep 2012, Lawrence Paulson wrote:
> I'm only talking about cases where “show" must inevitably fail.
> Fortunately, such situations are rare, but if they can easily be
> detected, they should be. Larry
> On 5 Sep 2012, at 14:20, Lars Noschinski <noschinl at in.tum.de> wrote:
>> On 05.09.2012 15:13, Lawrence Paulson wrote:
>>> Fixing a variable that ought to be free is an error.
>>> Highlighting is useful, but you have to be quite alert to notice it. I
>>> seldom notice it except in really blatant situations, like the same
>>> variable highlighted in two different ways. If the context is simply
>>> wrong, the highlighting should be absolutely unmissable.
>> Indeed, a variable shadowed by mistake is quite hard to detect. But is there a clear rule whether a variable "ought to be free"? Shadowing has its legitimate use cases (e.g. I usually shadow the "n" in induction proofs on the naturals).
With the "case that must fail" we are getting back to the tendencies of
where I failed to explain basic observations how warnings and errors get a
slightly different meaning in the Prover IDE model.
Concerning fixes (and implicit type abstractions) you know my basic plan
already: highlight the situation in the source text in a way that tells
the user what is there, and the user can then see by himself if it is what
he had in mind or should have in mind.
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