Re: transpiling to low level C

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:
>

[...]
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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.

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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.

Janis