How to add qi::symbols in grammar?

Question

I am trying to use Boost.Spirit (V. 2.5) library to create a mini-calculator. Features I want to implement : - basic calculus (+,-,/,*), that works - some functions (like m

Answer 1

Huh, I've never actually added symbols from directly inside Semantic Actions myself (I prefer to build ASTs, and then traverse those).

The fact that you wrote it like this and the absence of a SSCCE had me blindsided for a moment. Turns out, I should just have ignored the circumstantial 'evidence' and went straight for the docs + win:

var_decl =
    qi::as_string [ lexeme [ ( ( alpha >> *( alnum | '_' ) ) - vars ) ] ]
        [ phx::bind(vars.add, _1) ];

or

var_decl =
     lexeme [ qi::raw [  ( alpha >> *( alnum | '_' ) ) - vars  ] ]
        [ phx::bind(vars.add, _1) ];

and some similar incantations will apply

Edit Here is the complete source, compiled on MSVC 2010, with boost 1.47:

• https://gist.github.com/1582163

Output:

T:\>cl /EHsc /I "c:\Program Files (x86)\boost\boost_1_47" test.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.30319.01 for 80x86
Copyright (C) Microsoft Corporation.  All rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 10.00.30319.01
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test.exe
test.obj

T:\>.\test.exe
**********************************************************
*                                                        *
*          Command interface for VideoTraction4          *
*                                                        *
**********************************************************

Type an expression...or [q or Q] to quit

3*4+7
-------------------------
Parsing succeeded
result = 19
-------------------------

---

On a slightly unrelated note: it looks kind-a funny that the exposed attribute of the var_decl rule appears to be char?

You might want to read up on auto-rules and the %= operator; Without %=, the presence of a Semantic Action will suppress all automatic attribute propagation. That is helpful in case the required customization points do not exist. As written, the exposed attribute will always be unassigned-to.