| """ Branching Strategies to Traverse a Tree """ | |
| from itertools import product | |
| from sympy.strategies.util import basic_fns | |
| from .core import chain, identity, do_one | |
| def top_down(brule, fns=basic_fns): | |
| """ Apply a rule down a tree running it on the top nodes first """ | |
| return chain(do_one(brule, identity), | |
| lambda expr: sall(top_down(brule, fns), fns)(expr)) | |
| def sall(brule, fns=basic_fns): | |
| """ Strategic all - apply rule to args """ | |
| op, new, children, leaf = map(fns.get, ('op', 'new', 'children', 'leaf')) | |
| def all_rl(expr): | |
| if leaf(expr): | |
| yield expr | |
| else: | |
| myop = op(expr) | |
| argss = product(*map(brule, children(expr))) | |
| for args in argss: | |
| yield new(myop, *args) | |
| return all_rl | |