# examples/yaml/Calc.eyp
%right  '='
%left   '-' '+'
%left   '*' '/'
%left   NEG
%right  '^'

%tree bypass

%lexer {
    s/^\s+(?:#.*)?//;      # skip whites

    return('NUM',$1) if s{^([0-9]+(?:\.[0-9]+)?)}{};
    return('VAR',$1) if s/^([A-Za-z][A-Za-z0-9_]*)//;
    return($1,$1)    if s/^(.)//s;
  }

%%

exp:
    %name NUM 
    NUM                
  | %name VAR
    VAR                
  | %name ASSIGN 
    var '=' exp        
  | %name PLUS
    exp '+' exp        
  | %name MINUS
    exp '-' exp        
  | %name TIMES
    exp '*' exp        
  | %name DIV
    exp '/' exp        
  | %name UMINUS
    '-' exp %prec NEG  
  | %name EXPON
    exp '^' exp        
  | '(' exp ')'        
;

var:
    %name VAR
       VAR
;
%%

=head1 SYNOPSIS

Compile this grammar with

   eyapp -b '' -B '' Calc.eyp

Run it with:

    ./Calc.pm -t -i -c 'a = 2*3' 

You'll get an output like this:

    ASSIGN(VAR[a],TIMES(NUM[2],NUM[3]))

If you want to produce a YAML description of the AST
use the option C<-y>:

 $ ./Calc.pm -y -c 'b = 2+a' 
  --- !!perl/hash:ASSIGN
  children:
    - !!perl/hash:VAR
      attr: b
      children: []
      token: VAR
    - !!perl/hash:PLUS
      children:
        - !!perl/hash:NUM
          attr: 2
          children: []
          token: NUM
        - !!perl/hash:VAR
          attr: a
          children: []
          token: VAR

Run C<./Calc.pm -h> to get this help.

=cut