Bastiaan at Veelo.net
Wed Mar 1 21:52:09 CET 2017
Just a follow-up. I have since added a longest match alternator to Pegged, and it now successfully parses all Extended Pascal source that I have tried (with few Prospero extensions). It is too slow though to be the basis for a compiler; at this point.
Let me know if anyone here wants to try, I can provide binaries. (The source is there of course, see below).
> On 18 Feb 2017, at 11:37, Bastiaan Veelo <Bastiaan at Veelo.net> wrote:
> The parser is online now as an example of Pegged:
> However, the "ordered choice” parsing in PEG is not a good solution to deal with the ambiguities in the Extended Pascal grammar. When I threw one of my Pascal sources at it, it just failed to parse. I will see if implementing a “longest match choice” makes a difference.
> Note that this project is not meant to be part of a robust traditional compiler. My interests are in transcompiling, and therefore I am not concerned with the quality of error messages or performance. Also, as I understand it, the gpc frontend already parses almost all of EP, so I am not at all sure that writing a new parser is worth while. But for me it is a nice subject to get acquainted with D and experience its powers.
>> On 16 Feb 2017, at 09:59, Bastiaan Veelo <Bastiaan at Veelo.net> wrote:
>> The parser is complete except the handling of ambiguities. But it is just that: a parser. The output is an AST.
>> I have meant to submit the grammar as an example to Pegged , I’ll see if I can find some time for that, together with an example parser.
>>  https://github.com/PhilippeSigaud/Pegged
>>> On 15 Feb 2017, at 21:20, John L. Ries <jries at salford-systems.com> wrote:
>>> I'm not at all sure we really want a trilingual compiler, but the parser
>>> is complete or nearly so, it's probably worth a look.
>>> John L. Ries |
>>> Salford Systems |
>>> Phone: (619)543-8880 x107 |
>>> or (435)867-8885 |
>>> On Wed, 15 Feb 2017, Bastiaan Veelo wrote:
>>>> I wrote a recursive descent parser for Extended Pascal in the D language
>>>> using the Pegged library, which takes the rules of the standard almost
>>>> literally. I remember changing the order of options in some rules, but I am
>>>> unsure whether that was for efficiency or for giving precedence to common
>>>> constructs. I do remember seeing ambiguities in variable access and function
>>>> access, which I imagine can be resolved by keeping a symbol table of earlier
>>>> My parser is an interesting project but turned out to be rather inefficient
>>>> at the moment. If there is an interest I will consider to put it online.
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