Syntax: Every producer must be named.
If the programmer did not provide a name [_i] is used (where [i] is the producer's position in the right hand side). This syntax modification actually simplifies the code: - There is no more on-the-fly naming of unnamed arguments. - Inlining is no more restricted to semantic actions that do not use $i. The patch is large because: - This change has an impact on many modules. - The expected results of the bench had to be updated.