from neatomatch import _, freevars, match
_a, _b = freevars(2)
def evaltree(tree):
return match(tree,
('+', _a, _b),
lambda: evaltree(~_a) + evaltree(~_b),
('*', _a, _b),
lambda: evaltree(~_a) * evaltree(~_b),
_a,
lambda: ~_a)
binarytree = ('+', 3, ('*', ('+', 1, 1), 5))
assert 13 == evaltree(binarytree)
- Matches based on
__len__and__iter__recursively checking for matching leaves. Actual types don't matter. - Uses
_to match anything - The pattern
(_a, _a)matches(3, 3)but not(3, 4) - The implementation is tiny
It's mostly for fixed length sequences, but can operate on variable length things with the help of slices:
def sum(xs):
return match((xs[0], xs[1:]),
(_a, []), lambda: ~_a,
(_a, _b), lambda: ~_a + sum(~_b))
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