Re: How to construct a BNF for a language mechanically and incrementally?

[Peng Yu]

On Tue, Dec 29, 2009 at 2:49 AM, Hans Aberg <address@hidden> wrote:
> On 29 Dec 2009, at 03:54, Peng Yu wrote:
>
>> It seems to me that to use bison I have to have a BNF first. I'm
>> reading Programming Language Pragmatics 3rd Ed (PLP3). What is not
>> clear to me is that how to construct the BNF for a language? Based on
>> my reading of PLP3, I haven't found a formal way to construct BNF.
>> What I understand is that, to construct a BNF, I'll have to think
>> about some examples written in the language and write the BNF based on
>> my experience.
>>
>> A language definition is usually evolving. It is not clear to me
>> whether it always affects the BNF incrementally if the language is
>> changed little by little.
>
> Much depends on what you want to do, and the methods are largely empirical.
>
> If you want to implement an already existing language, there is a chance
> there already is a grammar, if such can be done. Search on the net for
> "<language> Yaccable (LALR) grammar" and such. Check out the Usenet
> newsgroup comp.compilers and its FAQ published there monthly.
>
> I can still be difficult to produce a LALR(1) grammar. For C++/C see
>  http://www.parashift.com/c++-faq-lite/compiler-dependencies.html#faq-38.11
>  http://www.quut.com/c/ANSI-C-grammar-y.html
> For some languages, like Fortran, Bison/Flex are not a good at all.

Why Bison/Flex are not good at Fortran? What is special for Fortran's grammar?

> If you want to design your own language, it may suffice with starting with a
> small example, such as the calculator in the Bison manual, and then expand.
> Ideas can be input from sources like the grammar-like appendix in the C++
> standard, and other sources of the type of language you want to design.
>
>  Hans
>
>
>