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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Top 10 most common hard skills listed on resumes...
Date: Sat, 31 Aug 2024 15:10:07 -0700
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Bart <bc@freeuk.com> writes:

> On 30/08/2024 21:41, Keith Thompson wrote:
>
>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>
>>> Kaz Kylheku <643-408-1753@kylheku.com> writes:
>>>
>>>> On 2024-08-29, Ben Bacarisse <ben@bsb.me.uk> wrote:
>>>>
>>>>> Bart <bc@freeuk.com> writes:
>>>>>
>>>>>> I think that these (with x, y having compatible scalar types):
>>>>>>
>>>>>>     x + 1 = y;
>>>>>>     (x + 1) = y;         // in case above was parsed differently
>>>>>>
>>>>>> are both valid syntax in C. It will fail for a different reason:
>>>>>> an '+' term is not a valid lvalue.
>>>>>
>>>>> The compiler must tell you that neither is valid C.  That's
>>>>> because what is required on each side of assignment is not
>>>>> exactly the same thing.  It's a distraction to argue about why
>>>>> each is not valid C as both have errors that require diagnostic
>>>>> at compile time.
>>>>
>>>> Bart is only saying that it's valid syntax, not that it's valid C.
>>>>
>>>> According to the ISO C syntax (not taking into account contraints,
>>>> which are not syntax) that view is justified.
>>>
>>> The second line is syntactically well-formed.  The first line is
>>> not.
>>
>> Right, because the LHS of an assignment is a unary-expression.
>> `(x + 1)` can be parsed as a unary-expression, but `x + 1` cannot.
>
> AFAICT both terms are parsed the same way.
>
> Given this:
>
>    x + y = z;
>    (x + y) = z;
>
> My compiler produces the same AST for the LHS of '=' in both
> cases.

To understand why they are different, try drawing parse trees
rather than abstract syntax trees.

https://en.wikipedia.org/wiki/Parse_tree