start   <- expr %eof;

expr    <- add;

add     <- a:mult ( "+" b:mult {{ @matches[:a] += @matches[:b] }}
                  / "-" b:mult {{ @matches[:a] -= @matches[:b] }}
                  )* {{ @value = @matches[:a] }};

mult    <- a:log ( "*" b:log {{ @matches[:a] *= @matches[:b] }}
                 / "/" b:log {{ @matches[:a] /= @matches[:b] }}
                 )* {{ @value = @matches[:a] }};

log     <- LN a:log {{ @value = Math.log(@matches[:a]) }}
        /  value:atom;

atom    <- value:number
        /  OPEN value:expr CLOSE
        /  PI  {{ @value = Math::PI }}
        /  E   {{ @value = Math::E }};

number  <- float:(([0-9]* "." [0-9]+)([eE][-+]?[0-9]+)?)
                                {{ @value = @matches[:float].to_f }}
        /  int:([+-]?[0-9]+)     {{ @value = @matches[:int].to_i }};

LN      <- "ln" spacing;
OPEN    <- "(" spacing;
CLOSE   <- ")" spacing;

PI      <- "PI" spacing;
E       <- "E" spacing;

spacing <- [ \n\r\t\f]*;