parser bug: macro calls w/o parens in generator expressions

[StefanKarpinski]

julia> maximum([@elapsed sleep(1) for k = 1:3])
1.003554001

julia> maximum(@elapsed(sleep(1)) for k = 1:3)
1.006058621

julia> maximum(@elapsed sleep(1) for k = 1:3)
ERROR: syntax: unexpected ")"

[c42f]

Hmm. We want

:(@a k for k=1:2)            -> :(@a(k) for k=1:2)              (1)
:(@a k for k=1:2; k ; end)   -> :(@a(k, for k=1:2; k ; end))    (2)

Currently the comprehension version works by setting the inside-vect parser state to true so it can stop parsing the macro when seeing a 'for token in parse-space-separated-exprs. But this simple strategy won't work for generators because case (2) above is already valid syntax.

[JeffBezanson]

Yes, I'm not sure this can be resolved. We use syntax like @threads x for i = 1:n ... where the for loop is an argument to the macro. The only possibility is to parse it differently inside parentheses, but then we have an expression that can't be parenthesized without changing its parsing, which seems like a bad idea to me.

[c42f]

Yes I imagined an inside-parens state might make sense and something inside parse-space-separated-exprs would just need to look further ahead to determine whether a given occurrence of for is a prefix of a for loop, or a generator expression.

But I'm not sure that kind of look ahead is compatible with the structure of the parser? It rather looks like it isn't.