Simplify expression representation

Store simple (<operator>, <operand 1>, <operand 2>) tuples instead of
(<operator>, [list of operands]) tuples.

The thought process behind the original representation was to avoid
creating lots of nodes for long X && Y && Z && ... chains that sometimes
appear, and possibly speed up evaluation. In retrospect, it's pretty
bad, for the following reasons:

 1) _make_and() and _make_or() created lots of new merged lists instead
    of simply reusing the tuples already allocated for the
    subexpressions. This is slow and memory hungry.

 2) Any gain in evaluating long expressions would barely offset slower
    evaluation of short expressions.

 3) The code became more complex.

Most importantly, this change makes expressions more straightforward to
work with for people peeking into internals.

0 files changed, 0 insertions, 0 deletions