-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost- bounces@lists.boost.org] On Behalf Of Joel de Guzman Sent: Friday, September 03, 2010 8:14 PM To: boost@lists.boost.org Subject: Re: [boost] De Bruijn Bind (alternate bind syntax) Interest?
On 9/4/2010 10:40 AM, David Sankel wrote:
Assuming phoenix::outer is reinstated, and assuming we have predefined placeholders for the most common arities and scopes (e.g. 1..10 args and 1..3 scopes), the phoenix equivalent would then be:
for_each(_1, lambda [ push_back(_1, _2_1) ] )
Very close to your syntax.
Indeed we are converging. I like code that is made up of independently useful and simple pieces that are composed together in powerful ways.
Yep. That's the mantra of Phoenix.
Your lambda uses brackets and I'm assuming this is for sequencing zero argument procedures.
Yeah. It's use and syntax is historical. The intent is to be as close as possible to C++ and to somehow emulate C++ statements. It is used that way, e.g.:
if_(c) [ dothis() ] .else_ [ dothat() ]
If we're talking C++0x you could also use initializer-list constructors: auto con = if_( c ), then_ { dothis0(), dothis1(), dothis2() }, else_ { dothat0(), dothat1(), dothat2() }; For an Adam/Eve DSEL in C++ we used this syntax: sheet save_file = "save_file" == sheet { interface == section { var{"file_name"} == [](arg_map args){ return any(""); }, var{"file_type"} == "txt", (var{"password"} <= (var{"file_type"}, var{"password1"})) == [](arg_map args) { return args.get<string>("file_type") == "txt" ? any("") : args["password1"]; } // more constraints }, output == section { // more constraints }, invariant == section { // more constraints } }; Which is assuredly overkill for a DBB, but still an option for syntax. BTW, initializer lists work great for an inline JSON library, i.e., json myjson = dict { key{"foo"} == list [ "baz", "bif", list [ "bop", "quux" ], key{"baz"} == "bar" };
It's not only for the sake of being clever. More importantly, C++ users connect to this easily compared to other concocted means. It is instantly recognizable.
So I'd make a separate function which would be useful for that (Instead of brackets, I'd use normal function calls with variadic templates for the same effect).
So
seq(a,b,c...) => { a(); b(); c();...}
lambda would be kept simple, as a single argument, and maybe a lamseq could be
auto lamseq = lamAppPrim( seq );
And then we get a true equivalence:
for_each(_1, lamseq ( push_back(_1, _2_1) ) )
Why keep outer if you have scoped_argument?
Agreed. outer is(was) built on top of scoped_argument anyway.
Regards -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net
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