class SyntaxTree::Parser

def on_in(pattern, statements, consequent)

) -> In
(nil | In | Else) consequent
Statements statements,
untyped pattern,
| (
on_in: (RAssign pattern, nil statements, nil consequent) -> RAssign
:call-seq: 
def on_in(pattern, statements, consequent)
  # Here we have a rightward assignment
  return pattern unless statements
  beginning = consume_keyword(:in)
  ending = consequent || consume_keyword(:end)
  statements_start = pattern
  if (token = find_keyword_between(:then, pattern, statements))
    tokens.delete(token)
    statements_start = token
  end
  start_char =
    find_next_statement_start((token || statements_start).location.end_char)
  # Ripper ignores parentheses on patterns, so we need to do the same in
  # order to attach comments correctly to the pattern.
  if source[start_char] == ")"
    start_char = find_next_statement_start(start_char + 1)
  end
  statements.bind(
    self,
    start_char,
    start_char -
      line_counts[statements_start.location.start_line - 1].start,
    ending.location.start_char,
    ending.location.start_column
  )
  node =
    In.new(
      pattern: pattern,
      statements: statements,
      consequent: consequent,
      location: beginning.location.to(ending.location)
    )
  PinVisitor.visit(node, tokens)
  node
end