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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: transpiling to low level C
Date: Mon, 23 Dec 2024 13:28:38 -0800
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On 12/23/2024 12:46 AM, David Brown wrote:
> On 22/12/2024 20:41, Janis Papanagnou wrote:
>> On 22.12.2024 07:01, Waldek Hebisch wrote:
>>> Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:
>>>> On 21.12.2024 02:28, Tim Rentsch wrote:
>>>>> Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
>>>>>
>>>>>> On 16.12.2024 00:53, BGB wrote:
>>>>>>
>>>>>>> [...]
>>>>>>>
>>>>>>> Pretty much all higher level control flow can be expressed via goto.
>>>>>>
>>>>>> A 'goto' may be used but it isn't strictly *necessary*. What *is*
>>>>>> necessary, though, that is an 'if' (some conditional branch), and
>>>>>> either 'goto' or recursive functions.
>>>>>
>>>>> Conditional branches, including 'if', '?:', etc., are not strictly
>>>>> necessary either.
>>>>
>>>> No? - Can you give an example of your statement?
>>>
>>> Look at example that I posted (apparently neither you nor Tim
>>> looked at my posts where I explained in detail how to translate
>>> goto program (with conditional jumps) into program that contains
>>> no goto and no conditional jumps).
>>
>> I'm not sure but may have just skimmed over your "C" example if it
>> wasn't of interest to the point I tried to make (at that stage).
>>
>>> Or try to figure out how to do this knowing that C has function
>>> pointers.
>>
>> I will retry to explain what I tried to say... - very simply put...
>>
>> There's "Recursive Functions" and the Turing Machines "equivalent".
>> The "Recursive Functions" is the most powerful class of algorithms.
>> Formal Recursive Functions are formally defined in terms of abstract
>> mathematical formulated properties; one of these [three properties]
>> are the "Test Sets". (Here I can already stop.)
>>
>> But since we're not in a theoretical CS newsgroup I'd just wanted
>> to see an example of some common, say, mathematical function and
>> see it implemented without 'if' and 'goto' or recursion. - Take a
>> simple one, say, fac(n) = n! , the factorial function. I know how
>> I can implement that with 'if' and recursion, and I know how I can
>> implement that with 'while' (or 'goto').
>>
>> If I re-inspect your example upthread - I hope it was the one you
>> wanted to refer to - I see that you have removed the 'if' symbol
>> but not the conditional, the test function; there's still the
>> predicate (the "Test Set") present in form of 'int c2 = i < n',
>> and it's there in the original code, in the goto transformed code,
>> and in the function-pointer code. And you cannot get rid of that.
>>
>> Whether you have the test in an 'if', or in a ternary '?:', or
>> use it through a bool-int coercion as integer index to an indexed
>> function[-pointer] table; it's a conditional branch based on the
>> ("Test Set") predicate i<n. You showed in your example how to get
>> rid of the 'if' symbol, but you could - as expected - not get rid
>> of the actual test that is the substance of a conditional branch.
>>
>> I think that is what is to expect by the theory and the essence of
>> the point I tried to make.
>>
> 
> You are adding more restrictions than Tim had given.
> 
> We all know that for most non-trivial algorithms you need some kind of 
> repetition (loops, recursion, etc.) and some way to end that repetition. 
>   No one is claiming otherwise.
> 
> Tim ruled out &&, ||, ?:, goto, break, continue, if, for, while, switch, 
> do, labels, setjmp and longjmp.
> 
> He didn't rule out recursion, or the relational operators, or any other 
> part of C.
[...]

pseudo code

func_ptr icall = funcs[i % 3];

icall->you()

;^)