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

[Srinivas Nayak]

Dear All,

While using Follow* command from EBNF.Mod.txt
I saw that it prints "Non-follow symbols:"

I didn't get this.
What exactly we wanted it to print?
Aren't they follow symbols?

Kindly help me to understand this.


With thanks and best regards,

Yours sincerely,
Srinivas Nayak

Home: http://www.mathmeth.com/sn/
Blog: http://srinivas-nayak.blogspot.in/

On 07/20/2016 08:23 AM, Srinivas Nayak wrote:
> Dear All,
>
> My doubt came true.
> Beautifully the calculation of First and Follow
> is present in EBNF.Mod.txt.
> I don't know how to use those commands.
> But I am happy that even though First and Follow command
> is not discussed in the book, it is present in code.
> Hopefully these commands also notify user if language is not LL(1).
>
>
> With thanks and best regards,
>
> Yours sincerely,
> Srinivas Nayak
>
> Home: http://www.mathmeth.com/sn/
> Blog: http://srinivas-nayak.blogspot.in/
>
> On 07/19/2016 02:15 AM, John R. Strohm 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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>>> https://lists.inf.ethz.ch/mailman/listinfo/oberon
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