Flattening recursive lists in Grammar Kit: private, inner, upper, left

Answered

Created August 26, 2023 16:32

I have a grammar that looks like the following

rule ::= item (SEP rule?)

I would like to flatten it out so a rule is a list, is it possible to do so with inner, upper, or private modifiers? Or, should I hand-roll methods to access the grammar like a list?

Also, what does private mean with respect to precedence? I'd like to use it to flatten the hierarchy but worried it would change the order of evaluation and bork the grammar on something like this

ySegmentExclNat ::= ySegmentMulti | containedSegment | YNAME

Where multi must be evaluated first

here's a link to the grammar: https://github.com/kieda/yapping-intellij/blob/main/src/main/java/io/hostilerobot/yapping/parser/grammar/Yapping.bnf

2 comments

Karol Lewandowski

Created August 31, 2023 08:29

Hi,

I'm not sure about the meaning of:

rule ::= item (SEP rule?)

Did you mean:

rule ::= item (SEP rule)?

If so, why do you want to use recursion here? Why not using:

rule ::= item (SEP item)*

You will have a flat list in this case.

The private modifier doesn't change the precedence. If it is used, then the AST won't include a node for this rule, but directly the children.

kieda

Created August 31, 2023 18:43

Hey!

Yep - misplaced comma. It turns out using private works and does not change the precedence/priority. I need the recursive property for more advanced constructs that may begin with other constructs, like

data ::= Properties|(item data?)

This was remediated and flattened using

data ::= data_? 
private data_ ::= Properties|(item data_?)

I had reservations about private, as this doc seems to imply that private is used to define statements of the same priority. However it's probably more of a best practice rather than something that actually changes the functionality

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