input: Write a python function to compile a regex pattern that matches words starting with 'a', 'b', or 'c'.
  assert pattern.match('apple') is not None
  assert pattern.match('banana') is not None
  assert pattern.match('cherry') is not None
  assert pattern.match('dog') is None
output: def compile_regex_pattern():
      import re
      pattern = re.compile(r'^[abc]\w*')
      return pattern