def _parse_re(l: _Lexer) -> Regex:
word = _parse_word(l)
if l.peek() is None or l.peek() == ")":
return word
if l.peek() != "|":
raise ValueError(f'Expected "|" at {l.i}.')
l.consume("|")
return Or(word, _parse_re(l))
def _parse_part(l: _Lexer) -> Regex:
atom = _parse_atom(l)
if l.peek() == "*":
l.consume("*")
return Kleene(atom)
if l.peek() == "+":
l.consume("+")
return Plus(atom)
if l.peek() == "?":
l.consume("?")
return Maybe(atom)
return atom
def _parse_char(l: _Lexer, in_set=False) -> Char:
c = l.next()
if c == "\\":
if l.peek() is None:
raise ValueError(
"Unexpectedly reached end of string. Expected escaped character."
)
real_c = l.next()
return Char(real_c)
if in_set:
return Char(c)
if c in META_CHARACTERS:
raise ValueError(
f'Found "{c}" at {l.i-1}. The character is not valid in this context'
)
return Char(c)
def _parse_atom(l: _Lexer) -> Regex:
if l.peek() is None:
raise ValueError("Reached end of string, expected more.")
if l.peek() == "(":
return _parse_group(l)
if l.peek() == "[":
return _parse_set(l)
if l.peek() == ".":
l.consume(".")
return AstConstant.any
if l.peek() == "$":
l.consume("$")
return AstConstant.end_of_string
return _parse_char(l)
def _parse_items(l: _Lexer) -> List[Union[Char, Range]]:
items: List[Union[Char, Range]] = []
while l.peek() != "]":
c = _parse_char(l, in_set=True)
if l.peek() == "-":
l.consume("-")
end = _parse_char(l, in_set=True)
assert end != "]"
items.append(Range(c, end))
continue
items.append(c)
l.consume("]")
return items
def _parse_set(l: _Lexer) -> Union[PosSet, NegSet]:
l.consume("[")
if l.peek() == "^":
l.consume("^")
return NegSet(_parse_items(l))
return PosSet(_parse_items(l))
def _parse_group(l: _Lexer) -> Group:
l.consume("(")
re = _parse_re(l)
l.consume(")")
return Group(re)
def _parse_word(l: _Lexer) -> Regex:
part = _parse_part(l)
if l.peek() in ("|", ")") or l.peek() is None:
return part
return Concat(part, _parse_word(l))