Re: First-class citizens with only one member causing trouble.

I found another workaround I just don't understand. This works perfectly:

// Instructions
instruction = ( // Semicolon terminated instructions
                 ( function_call
                 | variable_declaration
                 | variable_assignment
                 | print_variable
                 | print_text
                 | scan_variable
                 ) > ';')
             // Non-semicolon terminated instructions
             | if_else
             | while_loop
             | for_loop
             | instruction_block;

but this doesn't even compile:

// Instructions
instruction = (function_call        > ';')
             | (variable_declaration > ';')
             | (variable_assignment  > ';')
             | (print_variable       > ';')
             | (print_text           > ';')
             | (scan_variable        > ';')
             | if_else
             | while_loop
             | for_loop
             | instruction_block;


On 29.07.2016 18:30, Florian Klemme wrote:
>
> Hi,
>
> I have a little compiler project in which Spirit Qi works just fine. 
> But there is one little change I'd like to accomplish that causes 
> quite some (compilation) trouble. Have a look at this code snippet.
>
> // Instructions
> instruction = (function_call        > ';')
>             | (variable_declaration > ';')
>             | (variable_assignment  > ';')
>             | print_variable // Implicit semicolon TODO!!!?
>             | print_text     // Implicit semicolon
>             | scan_variable  // Implicit semicolon
>             | if_else
>             | while_loop
>             | for_loop
>             | instruction_block;
>
> function_call        = function_name >> '(' > -(variable_name % ',') > 
> ')';
> variable_declaration = qi::lexeme["var"] > variable_name > (('=' > 
> expression) | qi::attr(expression::value_t{0u}));
> variable_assignment  = variable_name >> '=' > expression;
> print_variable       = qi::lexeme["print"] >> variable_name > ';';
> print_text           = qi::lexeme["print"] >> qi::lexeme['"' > 
> *(qi::char_ - '"') > '"'] > ';';
> scan_variable        = qi::lexeme["scan"] > variable_name > ';';
>
> Don't look to deep into what these rules are composed of, the only 
> thing that matters is that the first three rules have their trailing 
> ';' defined in the instruction rule and the others have their ';' in 
> the rule itself.
>
> I want to move all tailing ';' to the instruction rule as shown in the 
> first few lines. For the first three rules this hasn't been a problem. 
> The literal parser ';' doesn't affect the attribute of the rule so the 
> position shouldn't matter.
>
> But in fact, *appending any literal parser before any "// Implicit 
> semicolon" comment causes a compilation error*. It took me some time 
> to figure out why this is not a problem with the other rules. It turns 
> out the problem is that the attribute of the problematic three rules 
> are first-class citizens with only one member (which happens to be a 
> string, not sure if this is relevant).
>
> So the following ugly workaround actually leads to a compiling (and 
> working) solution. By just adding a second member to the attribute of 
> the rule.
>
> diff --git a/bf/compiler.cpp b/bf/compiler.cpp
> index 6f83c00..7cea53a 100644
> --- a/bf/compiler.cpp
> +++ b/bf/compiler.cpp
> @@ -103,6 +103,7 @@ namespace instruction {
>
>      struct print_variable_t {
>          std::string variable_name;
> +        int         dummy;
>      };
>
>      struct print_text_t {
> @@ -253,7 +254,8 @@ BOOST_FUSION_ADAPT_STRUCT(
>
>  BOOST_FUSION_ADAPT_STRUCT(
>          bf::instruction::print_variable_t,
> -        (std::string, variable_name))
> +        (std::string, variable_name)
> +        (int,         dummy))
>
>  BOOST_FUSION_ADAPT_STRUCT(
>          bf::instruction::print_text_t,
> @@ -451,7 +453,7 @@ struct grammar : qi::grammar<iterator, 
> program_t(), ascii::space_type> {
>          instruction = (function_call        > ';')
>                      | (variable_declaration > ';')
>                      | (variable_assignment  > ';')
> -                    | print_variable // Implicit semicolon TODO!!!?
> +                    | (print_variable       > ';') // TODO!!!?
>                      | print_text     // Implicit semicolon
>                      | scan_variable  // Implicit semicolon
>                      | if_else
> @@ -462,7 +464,7 @@ struct grammar : qi::grammar<iterator, 
> program_t(), ascii::space_type> {
>          function_call        = function_name >> '(' > -(variable_name 
> % ',') > ')';
>          variable_declaration = qi::lexeme["var"] > variable_name > 
> (('=' > expression) | qi::attr(expression::value_t{0u}));
>          variable_assignment  = variable_name >> '=' > expression;
> -        print_variable       = qi::lexeme["print"] >> variable_name > 
> ';';
> +        print_variable       = qi::lexeme["print"] >> variable_name > 
> qi::attr(0);
>          print_text           = qi::lexeme["print"] >> qi::lexeme['"' 
> > *(qi::char_ - '"') > '"'] > ';';
>          scan_variable        = qi::lexeme["scan"] > variable_name > ';';
>          if_else              = qi::lexeme["if"] > '(' > expression > 
> ')' > instruction > -(qi::lexeme["else"] > instruction);
>
> Have a look at https://github.com/Kruecke/BFGenerator if you want to 
> check out the whole code. The critical section is this one: 
> https://github.com/Kruecke/BFGenerator/blob/master/bf/compiler.cpp#L454. 
> The workaround is committed in a branch as well: 
> https://github.com/Kruecke/BFGenerator/compare/semicolon_workaround. 
> If you want to run the code, make sure to run "make test" as the other 
> rules don't compile this piece of code at the moment.
>
> Please let me know if you have any idea how to fix this problem or 
> what mistake I might have made. I am thankful for any ideas. Or is 
> there a chance that this is a bug in Spirit Qi?
>
> I tested this with different versions of Boost as well as different 
> versions of gcc and msvc. C++14 support is required.
>
> Florian
>
>
>
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>
>
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