LEPL递归解析器-技术圈

LEPL递归解析器

联合创作 · 2023-10-01 04:46

LEPL是一个用 Python 开发的向下递归解析器。It is based on parser combinator libraries popular in functional programming, but also exploits Python language features. Operators provide a friendly syntax, and the consistent use of generators supports full backtracking and resource management. Backtracking implies that a wide variety of grammars are supported; appropriate memoisation ensures that even left-recursive grammars terminate.

>>> from lepl import *

>>> class Term(Node): pass
>>> class Factor(Node): pass
>>> class Expression(Node): pass

>>> expr   = Delayed()
>>> number = Digit()[1:,...]                          > 'number'
>>> spaces = Drop(Regexp(r'\s*'))

>>> with Separator(spaces):
>>>     term    = number | '(' & expr & ')'           > Term
>>>     muldiv  = Any('*/')                           > 'operator'
>>>     factor  = term & (muldiv & term)[:]           > Factor
>>>     addsub  = Any('+-')                           > 'operator'
>>>     expr   += factor & (addsub & factor)[:]       > Expression
>>>     line    = expr & Eos()

>>> parser = line.parse_string
>>> parser('1 + 2 * (3 + 4 - 5)')[0]

Expression
 +- Factor
 |   +- Term
 |   |   `- number '1'
 |   `- ' '
 +- operator '+'
 +- ' '
 `- Factor
     +- Term
     |   `- number '2'
     +- ' '
     +- operator '*'
     +- ' '
     `- Term
         +- '('
         +- Expression
         |   +- Factor
         |   |   +- Term
         |   |   |   `- number '3'
         |   |   `- ' '
         |   +- operator '+'
         |   +- ' '
         |   +- Factor
         |   |   +- Term
         |   |   |   `- number '4'
         |   |   `- ' '
         |   +- operator '-'
         |   +- ' '
         |   `- Factor
         |       `- Term
         |           `- number '5'
         `- ')

编辑