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375 lines
13 KiB
Python
375 lines
13 KiB
Python
#-------------------------------------------------------------------------------
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# Parser for ASDL [1] definition files. Reads in an ASDL description and parses
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# it into an AST that describes it.
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#
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# The EBNF we're parsing here: Figure 1 of the paper [1]. Extended to support
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# modules and attributes after a product. Words starting with Capital letters
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# are terminals. Literal tokens are in "double quotes". Others are
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# non-terminals. Id is either TokenId or ConstructorId.
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#
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# module ::= "module" Id "{" [definitions] "}"
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# definitions ::= { TypeId "=" type }
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# type ::= product | sum
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# product ::= fields ["attributes" fields]
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# fields ::= "(" { field, "," } field ")"
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# field ::= TypeId ["?" | "*"] [Id]
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# sum ::= constructor { "|" constructor } ["attributes" fields]
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# constructor ::= ConstructorId [fields]
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#
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# [1] "The Zephyr Abstract Syntax Description Language" by Wang, et. al. See
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# http://asdl.sourceforge.net/
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#-------------------------------------------------------------------------------
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from collections import namedtuple
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import re
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__all__ = [
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'builtin_types', 'parse', 'AST', 'Module', 'Type', 'Constructor',
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'Field', 'Sum', 'Product', 'VisitorBase', 'Check', 'check']
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# The following classes define nodes into which the ASDL description is parsed.
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# Note: this is a "meta-AST". ASDL files (such as Python.asdl) describe the AST
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# structure used by a programming language. But ASDL files themselves need to be
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# parsed. This module parses ASDL files and uses a simple AST to represent them.
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# See the EBNF at the top of the file to understand the logical connection
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# between the various node types.
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builtin_types = {'identifier', 'string', 'bytes', 'int', 'object', 'singleton'}
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class AST:
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def __repr__(self):
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raise NotImplementedError
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class Module(AST):
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def __init__(self, name, dfns):
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self.name = name
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self.dfns = dfns
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self.types = {type.name: type.value for type in dfns}
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def __repr__(self):
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return 'Module({0.name}, {0.dfns})'.format(self)
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class Type(AST):
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def __init__(self, name, value):
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self.name = name
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self.value = value
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def __repr__(self):
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return 'Type({0.name}, {0.value})'.format(self)
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class Constructor(AST):
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def __init__(self, name, fields=None):
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self.name = name
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self.fields = fields or []
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def __repr__(self):
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return 'Constructor({0.name}, {0.fields})'.format(self)
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class Field(AST):
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def __init__(self, type, name=None, seq=False, opt=False):
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self.type = type
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self.name = name
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self.seq = seq
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self.opt = opt
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def __repr__(self):
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if self.seq:
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extra = ", seq=True"
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elif self.opt:
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extra = ", opt=True"
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else:
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extra = ""
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if self.name is None:
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return 'Field({0.type}{1})'.format(self, extra)
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else:
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return 'Field({0.type}, {0.name}{1})'.format(self, extra)
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class Sum(AST):
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def __init__(self, types, attributes=None):
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self.types = types
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self.attributes = attributes or []
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def __repr__(self):
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if self.attributes:
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return 'Sum({0.types}, {0.attributes})'.format(self)
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else:
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return 'Sum({0.types})'.format(self)
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class Product(AST):
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def __init__(self, fields, attributes=None):
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self.fields = fields
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self.attributes = attributes or []
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def __repr__(self):
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if self.attributes:
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return 'Product({0.fields}, {0.attributes})'.format(self)
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else:
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return 'Product({0.fields})'.format(self)
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# A generic visitor for the meta-AST that describes ASDL. This can be used by
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# emitters. Note that this visitor does not provide a generic visit method, so a
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# subclass needs to define visit methods from visitModule to as deep as the
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# interesting node.
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# We also define a Check visitor that makes sure the parsed ASDL is well-formed.
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class VisitorBase(object):
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"""Generic tree visitor for ASTs."""
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def __init__(self):
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self.cache = {}
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def visit(self, obj, *args):
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klass = obj.__class__
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meth = self.cache.get(klass)
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if meth is None:
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methname = "visit" + klass.__name__
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meth = getattr(self, methname, None)
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self.cache[klass] = meth
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if meth:
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try:
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meth(obj, *args)
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except Exception as e:
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print("Error visiting %r: %s" % (obj, e))
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raise
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class Check(VisitorBase):
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"""A visitor that checks a parsed ASDL tree for correctness.
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Errors are printed and accumulated.
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"""
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def __init__(self):
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super(Check, self).__init__()
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self.cons = {}
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self.errors = 0
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self.types = {}
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def visitModule(self, mod):
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for dfn in mod.dfns:
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self.visit(dfn)
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def visitType(self, type):
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self.visit(type.value, str(type.name))
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def visitSum(self, sum, name):
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for t in sum.types:
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self.visit(t, name)
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def visitConstructor(self, cons, name):
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key = str(cons.name)
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conflict = self.cons.get(key)
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if conflict is None:
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self.cons[key] = name
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else:
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print('Redefinition of constructor {}'.format(key))
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print('Defined in {} and {}'.format(conflict, name))
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self.errors += 1
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for f in cons.fields:
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self.visit(f, key)
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def visitField(self, field, name):
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key = str(field.type)
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l = self.types.setdefault(key, [])
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l.append(name)
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def visitProduct(self, prod, name):
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for f in prod.fields:
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self.visit(f, name)
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def check(mod):
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"""Check the parsed ASDL tree for correctness.
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Return True if success. For failure, the errors are printed out and False
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is returned.
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"""
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v = Check()
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v.visit(mod)
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for t in v.types:
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if t not in mod.types and not t in builtin_types:
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v.errors += 1
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uses = ", ".join(v.types[t])
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print('Undefined type {}, used in {}'.format(t, uses))
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return not v.errors
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# The ASDL parser itself comes next. The only interesting external interface
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# here is the top-level parse function.
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def parse(filename):
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"""Parse ASDL from the given file and return a Module node describing it."""
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with open(filename) as f:
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parser = ASDLParser()
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return parser.parse(f.read())
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# Types for describing tokens in an ASDL specification.
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class TokenKind:
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"""TokenKind is provides a scope for enumerated token kinds."""
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(ConstructorId, TypeId, Equals, Comma, Question, Pipe, Asterisk,
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LParen, RParen, LBrace, RBrace) = range(11)
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operator_table = {
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'=': Equals, ',': Comma, '?': Question, '|': Pipe, '(': LParen,
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')': RParen, '*': Asterisk, '{': LBrace, '}': RBrace}
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Token = namedtuple('Token', 'kind value lineno')
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class ASDLSyntaxError(Exception):
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def __init__(self, msg, lineno=None):
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self.msg = msg
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self.lineno = lineno or '<unknown>'
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def __str__(self):
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return 'Syntax error on line {0.lineno}: {0.msg}'.format(self)
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def tokenize_asdl(buf):
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"""Tokenize the given buffer. Yield Token objects."""
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for lineno, line in enumerate(buf.splitlines(), 1):
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for m in re.finditer(r'\s*(\w+|--.*|.)', line.strip()):
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c = m.group(1)
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if c[0].isalpha():
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# Some kind of identifier
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if c[0].isupper():
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yield Token(TokenKind.ConstructorId, c, lineno)
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else:
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yield Token(TokenKind.TypeId, c, lineno)
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elif c[:2] == '--':
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# Comment
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break
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else:
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# Operators
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try:
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op_kind = TokenKind.operator_table[c]
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except KeyError:
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raise ASDLSyntaxError('Invalid operator %s' % c, lineno)
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yield Token(op_kind, c, lineno)
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class ASDLParser:
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"""Parser for ASDL files.
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Create, then call the parse method on a buffer containing ASDL.
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This is a simple recursive descent parser that uses tokenize_asdl for the
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lexing.
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"""
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def __init__(self):
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self._tokenizer = None
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self.cur_token = None
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def parse(self, buf):
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"""Parse the ASDL in the buffer and return an AST with a Module root.
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"""
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self._tokenizer = tokenize_asdl(buf)
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self._advance()
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return self._parse_module()
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def _parse_module(self):
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if self._at_keyword('module'):
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self._advance()
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else:
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raise ASDLSyntaxError(
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'Expected "module" (found {})'.format(self.cur_token.value),
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self.cur_token.lineno)
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name = self._match(self._id_kinds)
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self._match(TokenKind.LBrace)
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defs = self._parse_definitions()
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self._match(TokenKind.RBrace)
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return Module(name, defs)
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def _parse_definitions(self):
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defs = []
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while self.cur_token.kind == TokenKind.TypeId:
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typename = self._advance()
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self._match(TokenKind.Equals)
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type = self._parse_type()
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defs.append(Type(typename, type))
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return defs
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def _parse_type(self):
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if self.cur_token.kind == TokenKind.LParen:
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# If we see a (, it's a product
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return self._parse_product()
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else:
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# Otherwise it's a sum. Look for ConstructorId
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sumlist = [Constructor(self._match(TokenKind.ConstructorId),
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self._parse_optional_fields())]
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while self.cur_token.kind == TokenKind.Pipe:
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# More constructors
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self._advance()
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sumlist.append(Constructor(
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self._match(TokenKind.ConstructorId),
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self._parse_optional_fields()))
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return Sum(sumlist, self._parse_optional_attributes())
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def _parse_product(self):
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return Product(self._parse_fields(), self._parse_optional_attributes())
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def _parse_fields(self):
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fields = []
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self._match(TokenKind.LParen)
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while self.cur_token.kind == TokenKind.TypeId:
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typename = self._advance()
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is_seq, is_opt = self._parse_optional_field_quantifier()
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id = (self._advance() if self.cur_token.kind in self._id_kinds
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else None)
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fields.append(Field(typename, id, seq=is_seq, opt=is_opt))
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if self.cur_token.kind == TokenKind.RParen:
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break
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elif self.cur_token.kind == TokenKind.Comma:
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self._advance()
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self._match(TokenKind.RParen)
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return fields
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def _parse_optional_fields(self):
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if self.cur_token.kind == TokenKind.LParen:
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return self._parse_fields()
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else:
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return None
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def _parse_optional_attributes(self):
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if self._at_keyword('attributes'):
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self._advance()
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return self._parse_fields()
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else:
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return None
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def _parse_optional_field_quantifier(self):
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is_seq, is_opt = False, False
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if self.cur_token.kind == TokenKind.Asterisk:
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is_seq = True
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self._advance()
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elif self.cur_token.kind == TokenKind.Question:
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is_opt = True
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self._advance()
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return is_seq, is_opt
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def _advance(self):
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""" Return the value of the current token and read the next one into
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self.cur_token.
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"""
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cur_val = None if self.cur_token is None else self.cur_token.value
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try:
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self.cur_token = next(self._tokenizer)
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except StopIteration:
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self.cur_token = None
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return cur_val
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_id_kinds = (TokenKind.ConstructorId, TokenKind.TypeId)
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def _match(self, kind):
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"""The 'match' primitive of RD parsers.
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* Verifies that the current token is of the given kind (kind can
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be a tuple, in which the kind must match one of its members).
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* Returns the value of the current token
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* Reads in the next token
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"""
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if (isinstance(kind, tuple) and self.cur_token.kind in kind or
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self.cur_token.kind == kind
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):
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value = self.cur_token.value
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self._advance()
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return value
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else:
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raise ASDLSyntaxError(
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'Unmatched {} (found {})'.format(kind, self.cur_token.kind),
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self.cur_token.lineno)
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def _at_keyword(self, keyword):
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return (self.cur_token.kind == TokenKind.TypeId and
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self.cur_token.value == keyword)
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