patterns.py

@patterns
def factorial():
    with 0: 1
    with n:
          if n is int: n * factorial(n-1)
          if n is not int: raise ValueError("Int needed")
    with []: []
    with [x] + xs: [factorial(x)] + factorial(xs)
    with {'n': n, 'f': f}: f(factorial(n))

You can just write

@patterns
def factorial():
    if 0: 1
    if n is int: n * factorial(n-1)
    if n is not int: raise ValueError("Int needed")
    if []: []
    if [x] + xs: [factorial(x)] + factorial(xs)
    if {'n': n, 'f': f}: f(factorial(n))

If you want more complicated logic.

@patterns
def list_sum():
    with [x]+xs:        
        if x in str: list_sum([int(x)]+xs)
        if x > 10: x + list_sum(xs)