expression parsing zzz

operator priority

1. operator *, /
2. operator +, -
3. operator |, ~, &
4. operator ==, <, >, <=, >=, !=
5. operator = and derivatives

then while parsing expression (right to left):
  2 + a * b - c

  1. b - c: operator- compared to operator*; operator* wins. no action taken.
  2. a * b: operator* compared to operator+; operator* wins. expression branched into subexpression.
  3. 2 + subexpression(a * b): first statement. expression branched into subexpression.

  second pass:

  1. subexpression(2 + subexpression(a * b)) - c: first statement. expression branched into subexpression.
  end of parsing.