[Agda] Checking termination is not sufficiently exploratory.

[a.j.rouvoet]

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
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>>
>>
>>
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>
> -- 
> Serge Leblanc
> ------------------------------------------------------------------------
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>
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