calculator.yalr

option code.main    true;
// This will be inserted close to the top of the file
verbatim file.top <%{
#include <map>
}%>

verbatim namespace.top <%{
std::map<std::string, float> variables;
}%>

skip WS   r:\s+ ;

// basically here so that it is prefered to VARIABLE
// But, it also gives a chance to show case folding. 
// This will accept print or PRINT or PrInT, etc.
//
term PRINT 'print' @cfold ;

//
// zero to many underbar followed by a letter followed by as many digits,
// letters, underbars you want.
// allowed __a___
// not allowed __3
//
term <@lexeme> VARIABLE rm:_*[a-zA-Z][_a-zA-Z0-9]* ;

term <float>   NUMBER   r:-?\d*\.?\d+([eE][-+]?\d+)? <%{ return atof(lexeme.data()); }%>

//
// associativity will define the terminals for us.
//
associativity left '+' '-' '*' '/';
precedence 100 '+' '-';
precedence 200 '*' '/';

goal rule statement_list {
    => statement;
    => statement_list statement ;
}

rule statement { 
    => expression         <%{ std::cout << "(e)answer = " << _v1 << "\n"; }%> 
    => PRINT expression   <%{ std::cout << "(p)answer = " << _v2 << "\n"; }%> 
    => var:VARIABLE ':=' expr:expression <%{
        std::cout << "assigning " << expr << " to '" << var << "'\n"; 
        variables[var] = expr;
    }%>

}

rule <float> expression {
    => l:expression '+' r:expression <%{ return l + r; }%>
    => l:expression '-' r:expression <%{ return l - r; }%>
    => l:expression '*' r:expression <%{ return l * r; }%>
    => l:expression '/' r:expression <%{ return l / r; }%>
    => NUMBER             <%{ return _v1; }%>
    => VARIABLE           <%{ return variables[_v1]; }%>
    => '(' expression ')' <%{ return _v2; }%>
}