Pry v0.3.1 is out!

[Dmitry Olshansky via Digitalmars-d-announce]

On 1/17/17 1:16 PM, Bastiaan Veelo wrote:
> On Monday, 16 January 2017 at 22:29:01 UTC, Dmitry Olshansky wrote:
>> I think left-recursion is better handled at the grammar level.
>> What I currently have is parser combinators level where adding
>> this transformation is awkward and too much magic IMO.
>
> Handling left-recursion by grammar transformation often has unwanted
> side-effects (operator precedence) and eliminating indirect
> left-recursion this way can be impossible in practice. Depending on the
> complexity of the grammar, even identifying the recursive loop can be a
> challenge.

I do not suggest to change the grammar itself, I think that processing 
of the grammar may perform hidden transformations internally.

>
> The trouble is that one can be happily implementing a parser or
> designing a grammar when suddenly for some input the parser hangs
> indefinitely. Users are likely quick to blame the parser lib, while in
> fact it is the grammar that has left-recursion. Hitting that roadblock
> is a real bummer.
>
> In some cases the grammar is a given (by a standard for example) and
> transforming it to combat left-recursion can obfuscate it beyond
> recognition. Hardening Pegged to deal with the various kinds of
> left-recursion was very challenging, but easier than transforming the
> grammar I was dealing with (ISO 10206).

Interesting, what kind of hardening?

---
Dmitry Olshansky