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- """ 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
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