On 02/06/2026 14:05, Dan Cross wrote:
You're describing a 'Concrete Syntax Tree' or CST, versus AST.
Yes. "Concrete Syntax Tree" is another name for "Parse Tree".
Although in that case, I expect to see a discrete node for bracketed
expressions (ie. parenthesised), as those would also have a distinct
production in any formal grammar.
Was that not in the second parse tree diagram I presented?
Granted, I called it "expr", but as I noted, I was simplifying
heavily, mostly for space.
Personally I don't have much use for CSTs for a normal compiler, but
they might be useful for source-to-source translators, or programs that
do source refactoring, where you want to preserve extras such as
parentheses even if they're not strictly needed.
I think you're missing the point, here.
The question was whether, given some compiler, `a*b + c`
generates different code from `(a*b) + c`, and what it means for
the compiler to "remove the parentheses." I submit that, with
respect to the former, the answer is "very very unlikely" and
with respect to the latter, the question is a category error.
(Injecting the right parentheses for examples like `(a + b) * c' which
would have an AST like '(* (+ a b) c)' is surpringly tricky. Easier to
just follow the original source!
>
In any case, that still wouldnt't turn ((a+b)) back into the original;
you'd need a suitable CST.)
That's not related to what I was trying to convey.
- Dan C.
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