Editing Operator-precedence parser (section)

=== Example execution of the algorithm ===

An example execution on the expression 2 + 3 * 4 + 5 == 19 is as follows.  We give precedence 0 to equality expressions, 1 to additive expressions, 2 to multiplicative expressions.

''parse_expression_1'' (''lhs'' = 2, ''min_precedence'' = 0)
*  the lookahead token is +, with precedence 1.  the outer while loop is entered.
*  ''op'' is + (precedence 1) and the input is advanced
*  ''rhs'' is 3
*  the lookahead token is *, with precedence 2.  the inner while loop is entered.<br>''parse_expression_1'' (''lhs'' = 3, ''min_precedence'' = 2)
:*   the lookahead token is *, with precedence 2.  the outer while loop is entered.
::*    ''op'' is * (precedence 2) and the input is advanced
::*    ''rhs'' is 4
::*    the next token is +, with precedence 1.  the inner while loop is not entered.
::*    ''lhs'' is assigned 3*4 = 12
::*    the next token is +, with precedence 1.  the outer while loop is left.
:*   12 is returned.
*  the lookahead token is +, with precedence 1.  the inner while loop is not entered.
*  ''lhs'' is assigned 2+12 = 14
*  the lookahead token is +, with precedence 1.  the outer while loop is not left.
*  ''op'' is + (precedence 1) and the input is advanced
*  ''rhs'' is 5
*  the next token is ==, with precedence 0.  the inner while loop is not entered.
*  ''lhs'' is assigned 14+5 = 19
*  the next token is ==, with precedence 0.  the outer while loop is not left.
*  ''op'' is == (precedence 0) and the input is advanced
*  ''rhs'' is 19
*  the next token is ''end-of-line'', which is not an operator.  the inner while loop is not entered.
*  ''lhs'' is assigned the result of evaluating 19 == 19, for example 1 (as in the C standard).
*  the next token is ''end-of-line'', which is not an operator.  the outer while loop is left.
1 is returned.