solver. In conjunction, they easily found a tour of a 200x200 board:
that's 200**2 == 40,000 levels of backtracking. Explicitly resumable
generators allow that to be coded as easily as a recursive solver (easier,
actually, because different levels can use level-customized algorithms
without pain), but without blowing the stack. Indeed, I've never written
an exhaustive Tour solver in any language before that can handle boards so
large ("exhaustive" == guaranteed to find a solution if one exists, as
opposed to probabilistic heuristic approaches; of course, the age of the
universe may be a blip in the time needed!).
examples of use. These poke stuff not specifically targeted before, incl.
recursive local generators relying on nested scopes, ditto but also
inside class methods and rebinding instance vars, and anonymous
partially-evaluated generators (the N-Queens solver creates a different
column-generator for each row -- AFAIK this is my invention, and it's
really pretty <wink>). No problems, not even a new leak.
"return expr" instances in generators (which latter may be generators
due to otherwise invisible "yield" stmts hiding in "if 0" blocks).
This was fun the first time, but this has gotten truly ugly now.
that required explicitly calling LazyList.clear() in the two tests that
use LazyList (I added a LazyList Fibonacci generator too).
A real bitch: the extremely inefficient first version of the 2-3-5 test
*looked* like a slow leak on Win98SE, but it wasn't "really": it generated
so many results that the heap grew over 4Mb (tons of frames! the number
of frames grows exponentially in that test). Then Win98SE malloc() starts
fragmenting address space allocating more and more heaps, and the visible
memory use grew very slowly while the disk was thrashing like mad.
Printing fewer results (i.e., keeping the heap burden under 4Mb) made
that illusion vanish.
Looks like there's no hope for plugging the LazyList leaks automatically
short of adding frameobjects and genobjects to gc. OTOH, they're very
easy to break by hand, and they're the only *kind* of plausibly realistic
leaks I've been able to provoke.
Dilemma.
Good news: Some of this stuff is pretty sophisticated (read nuts), and
I haven't bumped into a bug yet.
Bad news: If I run the doctest in an infinite loop, memory is clearly
leaking.
unknown
Tim Peters