On Sat, May 29, 2021 at 09:51:22PM -0500, Bruce Gray wrote:
> > On May 29, 2021, at 5:57 PM, rir <[email protected]> wrote:
> > rule cmp_expression {
> > | <str_const> <cmp_op> <identifier>
> > | <num_const> <cmp_op> <identifier>
> > | ...
> > }
> I am not at all clear on what you are asking, so if none of my ideas are
> helpful,
> please consider adding more detail.
You understood more than you were confident of understanding.
Your number one describes my desire but it is not known to exist.
> 1. [...]
> . So, we do not have a convenient shortcut like:
> [...]
> | COMMUTATIVE( <str_const> <cmp_op> <identifier> )
> | COMMUTATIVE( <num_const> <cmp_op> <identifier> )
> | COMMUTATIVE( ... )
Your number two seems the common pattern. And is my intended
final approach (with variation for LHS and RHS overlap).
> 2. [...]
> rule cmp_operands_A {
> | <str_const>
> | <num_const>
> | ...
> }
> rule cmp_operands_B {
> | <identifier>
> | ...
> }
> rule cmp_expression {
> <cmp_operands_A> <cmp_op> <cmp_operands_B>
> | <cmp_operands_B> <cmp_op> <cmp_operands_A>
> }
Your number three is effectively the concise pattern I desire.
I think of it as list-op.
> 3. [...]
> rule cmp_operands { # ??? token instead of rule ???
> | <str_const>
> | <num_const>
> | <identifier>
> | ...
> }
> rule cmp_expression {
> <cmp_operands> ** 2 % <cmp_op>
> }
Your four is what I had and wanted to improve.
> 4. If none of that compresses the regex (maybe because not every <A> forms a
> valid pairing with *every* <B>),
> I would make each BopA variant live on the same line as its AopB cousin:
> rule cmp_expression {
> | <str_const> <cmp_op> <identifier> | <identifier> <cmp_op>
> <str_const>
> | <num_const> <cmp_op> <identifier> | <identifier> <cmp_op>
> <num_const>
> | ...
> }
> > I imagine that generally this is a useless question, which is
> > avoided by:
> >
> > rule cmp_expression {
> > <value_expression> <cmp_op> <value_expression>
> > }
> >
> > but here many tokens under value_expression exist but are not well
> > defined, nor known by me.
> This paragraph confuses me.
What is happening: I am working off of Postgresql documentation pages
to parse a specific small SQL codebase to support some code generation
( and to learn about grammars, etc.). Pg documentation is nearly all
top-notch. They seem to rename tokens just to clarify the larger
statement or construct. That hinders me from building my grammar from
the bottom up. SQL's <EXPRESSION> seems comprehensive but rarely worked
hard. With those issues and facts, I am just dealing with the specific
cases as they arrive while maintaining a SPoT and, hopefully, dispelling
my ignorance generally and about which tokens share identity.
Thanks for the prize behind door number three.
rir
> --
> Hope this helps,
> Bruce Gray (Util of PerlMonks)
>
>
