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"""Strategies to Traverse a Tree."""
from sympy.strategies.util import basic_fns
from sympy.strategies.core import chain, do_one
def top_down(rule, fns=basic_fns):
"""Apply a rule down a tree running it on the top nodes first."""
return chain(rule, lambda expr: sall(top_down(rule, fns), fns)(expr))
def bottom_up(rule, fns=basic_fns):
"""Apply a rule down a tree running it on the bottom nodes first."""
return chain(lambda expr: sall(bottom_up(rule, fns), fns)(expr), rule)
def top_down_once(rule, fns=basic_fns):
"""Apply a rule down a tree - stop on success."""
return do_one(rule, lambda expr: sall(top_down(rule, fns), fns)(expr))
def bottom_up_once(rule, fns=basic_fns):
"""Apply a rule up a tree - stop on success."""
return do_one(lambda expr: sall(bottom_up(rule, fns), fns)(expr), rule)
def sall(rule, 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):
return expr
else:
args = map(rule, children(expr))
return new(op(expr), *args)
return all_rl
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