Question

我正在尝试学习Racket，并且正在尝试重写Python过滤器。我的代码中有以下一对函数：

def dlv(text):
    """
    Returns True if the given text corresponds to the output of DLV
    and False otherwise.
    """
    return text.startswith("DLV") or \
           text.startswith("{") or \
           text.startswith("Best model")

def answer_sets(text):
    """
    Returns a list comprised of all of the answer sets in the given text.
    """
    if dlv(text):
        # In the case where we are processing the output of DLV, each
        # answer set is a comma-delimited sequence of literals enclosed
        # in {}
        regex = re.compile(r'\{(.*?)\}', re.MULTILINE)
    else:
        # Otherwise we assume that the answer sets were generated by
        # one of the Potassco solvers. In this case, each answer set
        # is presented as a comma-delimited sequence of literals,
        # terminated by a period, and prefixed by a string of the form
        # "Answer: #" where "#" denotes the number of the answer set.
        regex = re.compile(r'Answer: \d+\n(.*)', re.MULTILINE)
    return regex.findall(text)

据我所知，Racket中第一个函数的实现将是以下几点：

(define (dlv-input? text)
    (regexp-match? #rx"^DLV|^{|^Best model" text))

哪个似乎正常工作。关于第二个函数的实现，我目前已经提出以下内容（开始）：

(define (answer-sets text)
    (cond
        [(dlv-input? text) (regexp-match* #rx"{(.*?)}" text)]))

这是不正确的，因为regexp-match*给出了与正则表达式匹配的字符串列表，包括花括号。有谁知道如何获得与Python实现相同的行为？此外，任何关于如何使正则表达式“更好”的建议将非常感激。

Answer 1

你非常接近。您只需将#:match-select cadr添加到regexp-match来电：

(regexp-match* #rx"{(.*?)}" text #:match-select cadr)

默认情况下，#:match-select的值为car，返回整个匹配的字符串。 cadr选择第一个组，caddr选择第二个组等。有关详细信息，请参阅regexp-match* documentation。

从Python迁移到Racket（正则表达式库和“Racket Way”）

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