The current method for transforming sympy trees (used in the
printers, for example) can require some nested if-tests, even for some
simple cases like subtraction (addition of -1 multiplied by the first
arg), or division (mutiply by arg to the power of -1).
It would be nice to be able to represent and match on more complex
patterns in each 'if' branch
(like many functional languages). I've been working on a syntax for
doing this...
Small sample (this particular example converts to a python expression
tree)
def expr_to_py(e):
...
# subtraction
if m(Add, (Mul, S.NegativeOne, v.e1), v.e2):
# use v.e1 and v.e2 in constructing the target expression here
return py_expr(py_expr.PY_OP_MINUS, expr_to_py(v.e2),
expr_to_py(v.e1))
# addition
if m(Add, v.e1, v.e2):
return py_expr(py_expr.PY_OP_PLUS, expr_to_py(v.e1),
expr_to_py(v.e2))
Larger example and prototype implementation here:
https://gist.github.com/896417
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