如何为递归下降解析器的一部分编写代码？

Question

我正在寻找这个 Stack Overflow 问题的答案：

它要求执行以下操作，正如回复它的人解释的那样：

Write two functions,
ifblock
logic_expr
as part of a recursive descent parser in a language of your choosing.
<ifblock> --> if(<logic_expr>){<stmts>} [else {<stmts>}]
<logic_expr> --> <value> == <value> | <value> != <value>
For other non terminal symbols, 'stmts' and 'value' you are allowed to assume the existence of pre-written functions by the same names.

To get the next token from the input stream you can call 'lex()' which returns a code, as listed in the codes for the terminal symbols. Implement the 'ifblock' by requesting token codes by calling 'lex()' and to evaluate and match those with the required tokens according to the language grammar.

To evaluate the logical expression of the 'if' you need to step into a function 'logic_expr', which you need to write, for evaluating a logical expression as defined in the grammar, and you may assume that the non-terminal 'value' does already exist.

Answer 1

答案可能是这样的。当然，这只是语法解析器的截断伪代码，没有太多错误处理方式或 AST 构建器。

void parse() {
    while (!EOF)
       if (lex() == IF)
          ifblock()
       else // what is it?
}

void ifblock () {
    if (lex() != LP) 
       return_error;
    le = logic_expr();
    if (lex() != RP) 
       return_error;
    // parse statements in {}, optional else (if (lex() == ELSE) with {}
    // if no errors
    create_if_node(le, st, ...);
}

void logic_expr()
    v1 = value();
    op = lex();
    v2 = value();

    if (op == EQ)
       return create_eq_node(v1, v2);
    else if (op == NEQ)
       return create_neq_node(v1, v2);

    return_error();
}

如何为递归下降解析器的一部分编写代码？

How to write code for part of a recursive descent parser?

c

parsing

recursive-descent