[Agda] Checking termination is not sufficiently exploratory.

[Serge Leblanc]

In my opinion, a normal form verification phase could be added without
changing the termination checking algorithm.
Laŭ mi, normala kontrola fazo povus esti aldonita sen ŝangi la finiĝan
kontrolan algoritmon.

Sincere


On 2018-07-30 20:06, a.j.rouvoet wrote:
>
> I believe that you are right that the two snippets are equivalent, but
> it requires some computation to show that this is the case.
> The check that Agda runs on the other hand is very syntactic. This is
> indeed a limitation, but at least it ensures that checking for
> termination terminates ;-)
>
> On 07/30/2018 06:04 PM, Serge Leblanc wrote:
>> Yes, but you translat the code (toCostring ">>") ++ coSplit "(♭ xs)
>> to its normal form, it equals to '>' ∷ ♯ ('>' ∷ ♯ coSplit '(♭ xs)).
>> Right?
>> So, the recursive call is well protected by a constructor.
>>
>> Jes, sed vi plenumas la kodon (toCostring ">>") ++ coSplit″ (♭ xs)
>> ĝis sia normala formo, ĝi egalas al  '>' ∷ ♯ ('>' ∷ ♯ coSplit′ (♭
>> xs)). Ĉu ne ?
>> Do, la memsinkceva alvoko estas bone ŝirmi per konstruisto.
>>
>> On 2018-07-30 16:59, a.j.rouvoet wrote:
>>>
>>> For coSplit to pass the checker, the recursive invocation must
>>> appear guarded by a constructor.
>>> This is clearly the case in coSplit', but not necessarily in
>>> coSplit'' (e.g. when toString ">>" returns the empty costring).
>>>
>>>
>>> On 07/30/2018 04:55 PM, Serge Leblanc wrote:
>>>> Dear all,
>>>> Why the checking termination rejects the coSplit" function although
>>>> the coSplit' function is accepted ?
>>>> Why the checking termination so suspicious?
>>>> Sincerely
>>>>
>>>> Estimataj ĉiuj,
>>>> Kial la finiĝa kontrolo malakceptas la funkcion coSplit″ kvankam la
>>>> funkcio coSplit′ trafas ?
>>>> Kial la finiĝa kontrolo estas tiel malakceptanda ?
>>>> Sincere
>>>>
>>>>   coSplit′ : Costring → Costring
>>>>   coSplit′ [] = []
>>>>   coSplit′ (x ∷ xs) with x ≐ '!'
>>>>   ... | false = x ∷ ♯ coSplit′ (♭ xs)
>>>>   ... | true = '>' ∷ ♯ ('>' ∷ ♯ coSplit′ (♭ xs))
>>>>
>>>>   coSplit″ : Costring → Costring
>>>>   coSplit″ [] = []
>>>>   coSplit″ (x ∷ xs) with x ≐ '!'
>>>>   ... | false = x ∷ ♯ coSplit″ (♭ xs)
>>>>   ... | true = (toCostring ">>") ++ coSplit″ (♭ xs)
>>>>
>>>>   main = run $ ♯ getContents >>= λ s → ♯ (putStrLn∞ ∘ coSplit′) s
>>>>
>>>> -- 
>>>> Serge Leblanc
>>>> ------------------------------------------------------------------------
>>>> gpg --search-keys 0x67B17A3F
>>>> Fingerprint = 2B2D AC93 8620 43D3 D2C2 C2D3 B67C F631 67B1 7A3F
>>>>
>>>>
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>>>
>>>
>>>
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>>
>> -- 
>> Serge Leblanc
>> ------------------------------------------------------------------------
>> gpg --search-keys 0x67B17A3F
>> Fingerprint = 2B2D AC93 8620 43D3 D2C2 C2D3 B67C F631 67B1 7A3F
>>
>>
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>
>
>
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-- 
Serge Leblanc
------------------------------------------------------------------------
gpg --search-keys 0x67B17A3F
Fingerprint = 2B2D AC93 8620 43D3 D2C2 C2D3 B67C F631 67B1 7A3F
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