[Oberon] How2 calculate First and Follow and check if LL(1)

[Aubrey.McIntosh at alumni.utexas.net]

Coco does calculate first and follow sets.  I think there is a distinction
that they are static and not dynamic, but I don't have the experience to
discuss it, it is just something I saw in the documentation a decade ago.



On Mon, Jul 18, 2016 at 3:45 PM, John R. Strohm <strohm at airmail.net> wrote:

> As I recall, ANTLR generates parsers for LL(1) languages.
>
> yacc generates parsers for LALR(1) languages.
>
> COCO/R generates parsers for LL(k) languages.  There is an old version for
> Oberon.
>
> Wirth strongly prefers handmade recursive descent parsers, in part because
> languages that can be parsed easily by a handmade recursive descent parser
> tend to be quite a bit simpler and cleaner than languages that "requires" a
> machine-built LR(1) (or higher: JOVIAL was LR(2), if I remember correctly)
> parser.  PASCAL, Modula-2, and Oberon certainly meet that criteria when
> compared to C and C++ and their ilk.
>
> --- sinu.nayak2001 at gmail.com wrote:
>
> From: Srinivas Nayak <sinu.nayak2001 at gmail.com>
> To: ETH Oberon and related systems <oberon at lists.inf.ethz.ch>
> Subject: Re: [Oberon] How2 calculate First and Follow and check if LL(1)
> Date: Mon, 18 Jul 2016 22:38:36 +0530
>
> Dear Jorg and John,
>
> You both are correct.
>
> At least I got to know that we have EBNF parsing program.
> But we don't have a program to calculate First and Follow.
> Otherwise, you already would have mentioned it...
>
> Nicely without mentioning the word LL(1), professor Wirth explained
> what should be the characteristics of a language,
> so that it can easily be parsed using recursive descent parsing.
> He gave 3-4 rules of thumb and manually calculated First and Follow.
>
> No doubt, with Oberon like small/elegant language,
> one doesn't need to use machine to calculate First and Follow
> and to check LL(1) mechanically. It can be done manually.
> Mechanically calculating First and Follow is mostly needed for
> table driven parsers. For us not.
>
> I could see, because of unwanted complexity, Wirth intentionally
> refrained from detailing those and using the mechanical means,
> which is never needed for language implementer, but rather
> needed for the language designer, when language is LL(1).
>
> But I was little curious if we already have any
> mechanized program; so that, in case I want to play
> creating dialects of Oberon, I will have easy means to check my dialect.
>
> Another angle to my query was, if these algorithms can easily be
> inter woven with our EBNF parser... Those books present the algorithm
> in purest form. But I wanted to know, if using attributed grammar
> and our EBNF parser, it is easy to get the job done... If yes,
> how should we start about it.
>
> And yes, from another angle, I wanted to know, if someone has ever tried
> to do so...
>
>
> With thanks and best regards,
>
> Yours sincerely,
> Srinivas Nayak
>
> Home: http://www.mathmeth.com/sn/
> Blog: http://srinivas-nayak.blogspot.in/
>
> On 07/18/2016 06:01 PM, John R. Strohm wrote:
> > Calculation of First and Follow is covered in the Green Dragon Book.
> I'd expect it to be covered in the later books as well.
> >
> > And, as always, Google is your FRIEND.  "first follow sets"
> >
> > -----Original Message----- From: Srinivas Nayak
> > Sent: Sunday, July 17, 2016 8:52 PM
> > To: ETH Oberon and related systems
> > Subject: [Oberon] How2 calculate First and Follow and check if LL(1)
> >
> > Dear All,
> >
> > Lets say I want to modify Oberon language.
> > I would then like to check if my modified language is LL(1).
> > Towards that end, I would also like to calculate First and
> > Follow set of symbols for each of my non-terminals.
> >
> > I see a nice program EBNF.Mod
> > How can I modify this program to
> > 1. calculate First and Follow set of symbols for each of my
> non-terminals.
> > 2. check if my language is LL(1)
> >
> >
> >
> > With thanks and best regards,
> >
> > Yours sincerely,
> > Srinivas Nayak
> >
> > Home: http://www.mathmeth.com/sn/
> > Blog: http://srinivas-nayak.blogspot.in/
> > --
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Aubrey McIntosh, Ph.D.
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