# calc.ry. An example expression parser lifted straight out of the bison
# info pages.

%{

## Any require statements go here. Methods or constants defined here
## will be part of the parser class.

%}

%token NUM
%left '-' '+'
%left '*' '/'
%left NEG     # negation--unary minus
%right '^'    # exponentiation

%%

input:    # empty string
        | input line
;

line:     '\n'
	| error '\n' # example error recovery--throw away everything before \n
        | exp '\n' { printf ("\t%.10g\n", _$1) }
;

exp:      NUM                { _$$ = _$1         }
        | exp '+' exp        { _$$ = _$1 + _$3   }
        | exp '-' exp        { _$$ = _$1 - _$3   }
        | exp '*' exp        { _$$ = _$1 * _$3   }
        | exp '/' exp        { _$$ = _$1 / _$3   }
        | '-' exp  %prec NEG { _$$ = -_$2        }
        | exp '^' exp        { _$$ = _$1 ** _$3  }
        | '(' exp ')'        { _$$ = _$2         }
	| '(' error ')'	     { _$$ = 1           }
	## example error recovery--a bad expression is interpreted as a 1
;

%%

## Ruby code here will be placed *after* the parser class definition.