如何用pyparsing解析缩进和dedents？

Question

这是Python语法的一个子集:

single_input: NEWLINE | simple_stmt | compound_stmt NEWLINE

stmt: simple_stmt | compound_stmt
simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE

small_stmt: pass_stmt
pass_stmt: 'pass'

compound_stmt: if_stmt
if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite]

suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT

(您可以在Python SVN存储库中阅读完整语法:http://svn.python.org/.../Grammar)

我试图用这个语法在Python中生成Python的解析器.我遇到的问题是如何将这些INDENT和DEDENT令牌表达为pyparsing对象.

以下是我实现其他终端的方法:

import pyparsing as p

string_start = (p.Literal('"""') | "'''" | '"' | "'")
string_token = ('\\' + p.CharsNotIn("",exact=1) | p.CharsNotIn('\\',exact=1))
string_end = p.matchPreviousExpr(string_start)

terminals = {
    'NEWLINE': p.Literal('\n').setWhitespaceChars(' \t')
        .setName('NEWLINE').setParseAction(terminal_action('NEWLINE')),
    'ENDMARKER': p.stringEnd.copy().setWhitespaceChars(' \t')
        .setName('ENDMARKER').setParseAction(terminal_action('ENDMARKER')),
    'NAME': (p.Word(p.alphas + "_", p.alphanums + "_", asKeyword=True))
        .setName('NAME').setParseAction(terminal_action('NAME')),
    'NUMBER': p.Combine(
            p.Word(p.nums) + p.CaselessLiteral("l") |
            (p.Word(p.nums) + p.Optional("." + p.Optional(p.Word(p.nums))) | "." + p.Word(p.nums)) +
                p.Optional(p.CaselessLiteral("e") + p.Optional(p.Literal("+") | "-") + p.Word(p.nums)) +
                p.Optional(p.CaselessLiteral("j"))
        ).setName('NUMBER').setParseAction(terminal_action('NUMBER')),
    'STRING': p.Combine(
            p.Optional(p.CaselessLiteral('u')) +
            p.Optional(p.CaselessLiteral('r')) +
            string_start + p.ZeroOrMore(~string_end + string_token) + string_end
        ).setName('STRING').setParseAction(terminal_action('STRING')),

    # I can't find a good way of parsing indents/dedents.
    # The Grammar just has the tokens NEWLINE, INDENT and DEDENT scattered accross the rules.
    # A single NEWLINE would be translated to NEWLINE + PEER (from pyparsing.indentedBlock()), unless followed by INDENT or DEDENT
    # That NEWLINE and IN/DEDENT could be spit across rule boundaries. (see the 'suite' rule)
    'INDENT': (p.LineStart() + p.Optional(p.Word(' '))).setName('INDENT'),
    'DEDENT': (p.LineStart() + p.Optional(p.Word(' '))).setName('DEDENT')
}

terminal_action 是一个返回相应解析操作的函数,具体取决于其参数.

我知道pyparsing.indentedBlock帮助函数,但我无法弄清楚如何在没有PEER令牌的情况下将其用于语法.

(看看pyparsing souce代码,看看我在说什么)

你可以在这里看到我的完整源代码:http://pastebin.ca/1609860

Answer 1

在pyparsing wiki 示例页面上有几个示例可以为您提供一些见解:

• pythonGrammarParser.py
• indentedGrammarExample.py

要使用pyparsing indentedBlock,我想你会定义suite为:

indentstack = [1]
suite = indentedBlock(stmt, indentstack, True)

请注意,indentedGrammarExample.py包含indentedBlock在pyparsing 中的前置日期,自己实现的缩进解析也是如此.