Hi Robin,
Well, my little pattern matching thing would see that as a "nonstandard"
operator (not binary or unary etc.) and consider it a suffix operator because
it begins with immediate left recursion. It may not be pretty, but here is what
I get from
rpexpression
: rpexpression rpexpression OPERATOR
| OPERAND
;
becomes
rpexpression : rpexpression_[0] ;
rpexpression_[int _p]
: rpexpression_primary
( ( {_p <= 3}?=> rpexpression OPERATOR ) )*
;
rpexpression_primary
: OPERAND
;
Does not look correct? I have to jump off and prepare for class :) If not, I
better add a note to look into it.
Ter
On Apr 13, 2011, at 10:37 AM, Robin Lee Powell wrote:
> On Wed, Apr 13, 2011 at 10:26:14AM -0700, Terence Parr wrote:
>> On Apr 12, 2011, at 12:31 PM, Laurence Tratt wrote:
>>> On Tue, Apr 12, 2011 at 08:47:42AM -0700, Terence Parr wrote:
>>>
>>> Dear Terence,
>>>
>>>> Only limitation is immediate-left-recur handled only. In my
>>>> experience, that's good enough :) No point in some complicated
>>>> algorithm when this covers any grammar I'd care about.
>>>
>>> A quick question: is any type of direct left recursion handled?
>>> I'm probably being an idiot here (it's my normal mode), but your
>>> wiki post suggests that this relies on the grammar being built
>>> in an "expression" sort-of way, but the above post suggested
>>> there might be a bit more flexibility?
>>
>> Hi. Yep, in the end, it was straightforward to convert any
>> immediate left recursion
>
> People keep saying that, but I can't seem to figure it out. I
> especially can't see any way to deal with left recursion that
> doesn't totally break the meaningfulness of the resulting parse
> tree.
>
> Here's the bane of my PEG existence, from the Lojban grammar; it's a
> very simple two-argument-only RPN calculator:
>
> rp-expression <- rp-expression rp-expression operator / operand
>
> I can't see any way to fix that that leaves the operators associated
> with their argumenst properly.
>
> I'd love some help, if people have time.
>
> -Robin
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