On Tue, Dec 29, 2009 at 2:49 AM, Hans Aberg <hab...@math.su.se> 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 > > > _______________________________________________ help-bison@gnu.org http://lists.gnu.org/mailman/listinfo/help-bison
