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