Wow. Glad to see that good idea ( http://www.mail-archive.com/[email protected]/msg01359.html ) haven't gone into void. Without need for extra syntax ( [> and <: when I played with it ) it looks much prettier.
[On Tue, Dec 9, 2008 at 10:34 AM, Slava Pestov <[EMAIL PROTECTED]> wrote: > The second new feature is a new syntax for defining locals. Inside > your :: word or lambda, you can now do this: > > ... :> foo > ... foo ... > > :> defines a local whose value is the top of the stack, for the > duration of the innermost lexical scope. It is equivalent to the > following: > > [let | foo [ ] ... foo ... ] > > Note that lambdas and lets can be expressed in terms of :> > > [| a b c | ... ] > [ :> c :> b :> a ... ] > > [let | a [ X ] b [ Y ] | ... ] > X :> a Y :> b ... ! assuming Y does not reference 'b' from an outer scope > > but it is considerably more concise for the common case where you word > only needs to define one local. The idea for this syntax has been at > the back of my mind for quite some time, but only a few days ago did > the need for it arise. I wanted to rewrite parts of locals for > improved compile-time performance; the main problem with the old > implementation was the translation for [let; > > [let | a [ X ] | Y ] > > would translate to the following > > X [| a | Y ] call > > However, the subsequent closure conversion step would introduce a lot > of nested quotations with currying, and the result was some rather > complex code which took a lot of work for the compiler to boil down to > efficient stack code. The new translation of [let in terms of :> makes > the path from locals code to machine code more direct. There is no > performance difference in the generated code, but compile time has > improved. The most drastic speedup has been with the peg.javascript > vocabulary, which would formerly take just over 3 minutes to load, and > now it loads in under 2 minutes. The code generated by the PEG library > makes heavy use of locals and inlining, so compile time performance > really matters here. There is still a lot of room for improvement > there, of course, but this was a big jump. > > Slava > > ------------------------------------------------------------------------------ > SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. > The future of the web can't happen without you. Join us at MIX09 to help > pave the way to the Next Web now. Learn more and register at > http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ > _______________________________________________ > Factor-talk mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/factor-talk > ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Factor-talk mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/factor-talk
