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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.c
Subject: Re: Top 10 most common hard skills listed on resumes...
Date: Thu, 29 Aug 2024 15:58:52 -0000 (UTC)
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On 2024-08-29, Ben Bacarisse <ben@bsb.me.uk> wrote:
> Kaz Kylheku <643-408-1753@kylheku.com> writes:
>
>> On 2024-08-29, Ben Bacarisse <ben@bsb.me.uk> wrote:
>>> Bart <bc@freeuk.com> writes:
>>>
>>>> On 29/08/2024 13:35, Ben Bacarisse wrote:
>>>>> Bart <bc@freeuk.com> writes:
>>>>
>>>>>> I explained that. LHS and RHS can be identical terms for assignment in
>>>>>> pretty much every aspect, but there are extra constraints on the LHS.
>>>>> So you use "exactly the same" to mean "exactly the same except for the
>>>>> differences".
>>>>
>>>> No, I do mean exactly the same, both in terms of syntax and (in my
>>>> implementations, which are likely typical) internal representation of those
>>>> terms.
>>>>
>>>> There are no differences other than where the type system says your code is
>>>> invalid. So are no differences when considering only valid programs.
>>>>
>>>> This program in my language:
>>>>
>>>>      42 := 42
>>>>
>>>> is valid syntax.
>>>
>>> So what?  We were talking about assignment in C.  You cut the two
>>> previous quotes where it was clear we were talking about C.  This is not
>>> an honest thing to do.  You are arguing for the sake if it, and in a
>>> dishonest way too.
>>
>> It's also valid syntax in C, with a constraint violation that can be
>> "caught later on" in an implementation of C, just like in Bart's
>> language.
>
> Have you taken Bart's bait and are now discussing a narrower context?
>
> The claim that C's assignment is symmetric and what is required on the
> two sides is exactly the same is junk.  C's assignment has different
> syntax on each side, and what is required is even more strict.

In the ISO C grammar for assignment, there is a "unary expression" on
the left and an "assignment expression" on the right. That's just a
particular factoring of the grammar that implementors don't have to
follow, if the correct results are produced.

Under a parser generator tool we could have a production rule like
expr '=' expr , where the '=' token has an elsewhere-declared
associativity and precedence.

The basic idea that the same syntactic kind of thing is on both sides of
a C assignment (with an additional lvalue constraint) is valid;
it's just not literally true if we are discussing the details of how
ISO C expresses the grammar.

-- 
TXR Programming Language: http://nongnu.org/txr
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