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Boost.Phoenix makes it easier to attach semantic actions. You just inline your lambda expressions:
p[phoenix-lambda-expression]
          Spirit.Qi provides some Boost.Phoenix
          placeholders to important information from the Attrib
          and Context that are otherwise
          fiddly to extract.
        
Spirit.Qi specific Phoenix placeholders
_1,
            _2...
            , _N
                Nth attribute of p
              
_valThe enclosing rule's synthesized attribute.
_r1,
            _r2...
            , _rNThe enclosing rule's Nth inherited attribute.
_a,
            _b...
            , _j
                The enclosing rule's local variables (_a
                refers to the first).
              
_pass
                Assign false to _pass to force a parser failure.
              
| ![[Important]](../../../images/important.png) | Important | 
|---|---|
| 
            All placeholders mentioned above are defined in the namespace  | 
For more detailed information about semantic actions see: here.