No one is against the existence of a formal grammar – and anyone is free to write one. Of course, for it to be really meaningful, you have to make sure it stays in sync with Julia's actual parser. The only ways I can think of to reliably make sure the parser and the grammar stay in sync is to (a) make the grammar definitive by switching to using a parser generator or (b) do what Jake did with JuliaParser.jl <https://github.com/jakebolewski/JuliaParser.jl> and automatically run both parsers on a large body of code (e.g. all packages) and make sure that the ASTs constructed are identical. Parser generators tend to be much slower than hand-coded parsers and Julia's grammar is slightly context sensitive in a way that most parser generators – especially the more efficient ones – can't handle. So (a) isn't really a practical option. Option (b) still requires a parser generator, but since that parser won't be used by Julia itself, it can be slow. This option would require:
1. A formal grammar (the easy part); 2. A parser generator that takes that formal grammar as input and produces AST; 3. Infrastructure for automatically parsing and checking a large body of Julia code. Again, step 2 is made tricky since most parser generators can't handle Julia's slightly context-sensitive grammar – so you might need to write your own parser generator infrastructure. So if someone – say you – really wants there to be a formal grammar for Julia that stays in sync with Julia's parser, then it would be great if they wrote one. And then wrote a parser generator based on it. And then set up some infrastructure to automatically check its output against the standard parser on all registered Julia packages. This is certainly possible, but I'm sure you can see why I think there are better ways for the people who are most qualified to do this – namely Jeff and Jake – to spend their time. I'm not saying this wouldn't be good to have, but it's just a lot of work for fairly little return. On Wed, Aug 20, 2014 at 12:36 PM, gentlebeldin <[email protected]> wrote: > Maybe there *are* drawbacks of ad-hoc parsers, after all. I don't want to > be offensive, really, I like Julia... but the absence of a formal > specification of the grammar is nothing to be proud of. > > Am Dienstag, 19. August 2014 01:39:53 UTC+2 schrieb Stefan Karpinski: >> >> That seems likely. >> >> On Aug 18, 2014, at 7:24 PM, Elliot Saba <[email protected]> wrote: >> >> Probably because of our special parsing of & in ccall invocations. >> -E >> >> >> On Mon, Aug 18, 2014 at 7:14 PM, Stefan Karpinski <[email protected]> >> wrote: >> >>> Yeah, I forget exactly why you can't to that with & but there's some >>> parsing ambiguity. >>> >>> >>> On Mon, Aug 18, 2014 at 6:33 PM, ggggg <[email protected]> wrote: >>> >>>> Ok, thanks. Although it doesn't seem to be the case for |, eg "|(true, >>>> false)" works out of the box. >>>> >>>> >>>> On Monday, August 18, 2014 4:24:31 PM UTC-6, Stefan Karpinski wrote: >>>> >>>>> This are some of those few operators that need parens to be used in >>>>> function call syntax: >>>>> >>>>> julia> (&)(3,5) >>>>> 1 >>>>> >>>>> julia> (|)(3,5) >>>>> 7 >>>>> >>>>> >>>>> This isn't required in unambiguous situations like as an argument to >>>>> another function: >>>>> >>>>> julia> reduce(|, 0:8) >>>>> 15 >>>>> >>>>> >>>>> >>>>> >>>>> On Mon, Aug 18, 2014 at 6:20 PM, ggggg <[email protected]> wrote: >>>>> >>>>>> Is there a named function that does what & does, eg "&(a,b) == a&b"? >>>>>> I actually want a multi argument version like "$(a,b,c...)". Also is >>>>>> that >>>>>> the name of that function is not "&" and "& is not overloadable? The same >>>>>> is not true of "|". >>>>>> >>>>>> *julia> **a = zeros(Bool,10);b=[randbool() for j=1:10];* >>>>>> >>>>>> *julia> **a&b==b* >>>>>> >>>>>> *false* >>>>>> >>>>>> *julia> **a|b==b* >>>>>> >>>>>> *true* >>>>>> >>>>>> *julia> **|(a,b)==b* >>>>>> >>>>>> *true* >>>>>> >>>>>> *julia> **&(a,b)==b* >>>>>> >>>>>> >>>>>> *ERROR: unsupported or misplaced expression & * >>>>>> *julia> **&(a,b) = a&b* >>>>>> >>>>>> *ERROR: syntax: invalid assignment location* >>>>>> >>>>>> Julia even seems to think & is a function >>>>>> >>>>>> *julia> **&* >>>>>> >>>>>> *& (generic function with 35 methods)* >>>>>> >>>>>> >>>>>> >>>>> >>> >>
