On Mon, 30 Sep 2013 19:04:32 +0200, Franck Ditter wrote: > Good approach of FP in Python, but two points make me crazy : 1. Tail > recursion is not optimized. We are in 2013, why ? This is known > technology (since 1960). And don't answer with "good programmers don't > use recursion", this is bullshit.
Tail recursion optimization isn't really that useful. There is a HUGE universe of recursive problems which are not tail-recursive, and so cannot be optimized at all, or at least not automatically. Instead of encouraging people to rewrite such code using tail-recursion, which usually ends up obfuscating the code and introducing subtle bugs, it is better to encourage them to rewrite it to be iterative instead of recursive. Or just use recursion -- in many cases (although not all), if you have to recurse so many times that you pass the limit, your code is probably doing something wrong. So tail-recursion optimization only helps in a tiny subset of recursive problems. Usually it doesn't help at all. And one cost is that you lose debugging information. Don't think of a single recursive function, where the traceback is extremely boring: py> f() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 2, in f File "<stdin>", line 2, in f [...] File "<stdin>", line 2, in f File "<stdin>", line 2, in f File "<stdin>", line 2, in f RuntimeError: maximum recursion depth exceeded Think of mutually recursive functions, where f calls g which calls h which sometimes calls f and sometimes calls g... Personally, I'm not 100% convinced by these arguments. I think having a runtime option to enable or disable tail recursive optimizations would make Python a better language. Not by a lot, but by a tiny bit. But the people who would actually do the work don't care enough to do it, and the people who say they care don't bother doing the work. > 2. Lambda-expression body is limited > to one expression. Why ? Nobody has come up with syntax that is unambiguous, would allow multiple statements in an expression, doesn't break backwards compatibility, and isn't ugly. Since lambda is just a convenience, not a necessity -- it almost got dropped from Python 3 -- it is not worth compromising on those design requirements just for multiple-statement lambdas. It simply isn't important enough. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
