[cfe-dev] Disambiguating C++ Lambdas and Objective-C Messages

[John Freeman]

Howdy Doug,

Based on recommendations, I'm looking at the following decision tree 
after seeing a '['.

if lang = C++
   if lang = Objective-C
     if lookahead indicates lambda
       parse_lambda
     else if lookahead indicates message
       parse_message
     else
       allocate lambda capture list
       if tentative parse of lambda successful
         finish_parse_lambda(list)
       else
         parse_message
   else
     parse_lambda
else if lang = Objective-C
   parse_message
else
   error

The parse_lambda and finish_parse_lambda functions will need to be 
different, although the first function could call the second.

Is it too much? Should I try something simpler? Should I try an 
alternative structure, like this:

if lang = C++ && lang != Objective-C
   parse_lambda
else if lang != C++ && lang = Objective-C
   parse_message
else if lang = C++ && lang = Objective-C
   if lookahead indicates lambda
     parse_lambda
   else if lookahead indicates message
     parse_message
   else
     allocate lambda capture list
     if tentative parse of lambda successful
       finish_parse_lambda(list)
     else
       parse_message
else
   error

Should I wrap the lookahead and the tentative parsing into a single 
TryParse* function? Perhaps it could return a valid but unusable 
ExprResult upon parsing a lambda with unrecoverable errors, and an 
invalid ExprResult when lookahead or tentative parsing indicated a 
message. If that does not fit within the convention for invalid/usable, 
could you please explain it?


- John