3 ms·

What I think stood out most as mistaken about Guido's post was his conflating recursion and recursive data structures in his third point. "For practical purpose

What I think stood out most as mistaken about Guido's post was his conflating recursion and recursive data structures in his third point. "For practical purposes, Python-style lists (which are flexible arrays, not linked lists), and sequences in general, are much more useful to start exploring the wonderful world of programming than recursion... Most of Python's library is written with sequences and iterators as fundamental building blocks (and dictionaries, of course), not linked lists, so you'd be locking yourself out of a lot of pre-defined functionality by not using lists or sequences." Well, chained cons cells are lists, too, and recursive functions are good for much more than operating over recursive data structures. Recursion is often the only simple solution in messy real world stuff. Just last week I wrote recursive code to do one of the most real-worldy and least Computer Science-y thing imaginable: get data from a public API. I didn't see any reasonable alternative to recursion. (But since that project was, sadly, not written in a language with TCO I am stuck with a function that's going to break if our little Twitter app gets popular, at which point I'll have to do unreasonable hack.) But I admire Guido and could be misinterpreting what he said.

dkarl 18y ago
I think what he meant is that beginners have an easier time with iterators and list indexing than with recursive techniques. An important target group for Python is beginners and non-programmers who do some programming in support of their primary work. That's why Guido values stack traces over tail call optimization. For Python, supporting beginners and amateurs is a higher goal than writing elegant functional code. Even for problems with elegant recursive solutions, beginners seem to find it easier to cobble together a more complicated loop-based solution than to find the simple recursive one. I know that makes everyone really sad :-( and maybe the long-term solution is to fix the school curriculum to teach programming earlier and better, but for now it's reality.
- herdrick 18y ago
  Good points. But favoring Python lists over recursion is like favoring chocolate over logging. However, I'm probably just playing gotcha here. My apologies to HN and Guido. My more important point is that recursion is good for real world stuff.
  - dkarl 17y ago
    Good points. But favoring Python lists over recursion is like favoring chocolate over logging. No, no, it's not at all, not when you approach it from Guido's point of view. To him, the crucial question is, "What's the right way for beginners to process data?" Python and its built-in data structures support iteration and list indexing because that's how beginners do it. Python does not support tail calls because Guido thinks it's a mistake to teach recursion to beginners. I think everyone is misunderstanding Guido's point because they just can't imagine anyone taking his point of view, so they imagine him saying something else. Joe Marshall even called Guido's main points (which he correctly identified, and then ungraciously caricatured) "a sideshow" and said the "true argument" is about the power of recursion. Sorry, Guido doesn't care about the power of recursion, because it isn't valuable to his target programmers, the programmers he wants to serve. He really thinks tail call support would be a very minor feature in Python because it's not important whether you can program in Python that way. He thinks complete stack trace information is very important because it makes things easy and transparent for beginners. That's what's important to Guido and, I would argue, to most Python programmers. When it comes to the future of Python, that's what matters, and Joe Marshall is the sideshow.
    - herdrick 17y ago
      Python's lists are just as good for recursion as Scheme's cons cells - the data structure doesn't really matter. That was my nitpicky point. I agree that Python's emphasis on beginner-friendliness was the smart choice and led, ironically, to its current dominance in numerical computation.
silentbicycle 17y ago
If you want to see a language which is stylistically very similar to Python* , but has TCO, check out Lua. In practice: you can easily add pre-tail-call tracing, you have the option of starting a debugging REPL on error, using iterators is very idiomatic, it makes implementing coroutines and fully-functional closures easier, etc. I happen to think the most significant benefit of TCO is being able to set up "looping" tail calls between multiple functions, but that's just me. * Somewhere between Python and Javascript, specifically.

dkarl 18y ago

I think what he meant is that beginners have an easier time with iterators and list indexing than with recursive techniques. An important target group for Python is beginners and non-programmers who do some programming in support of their primary work. That's why Guido values stack traces over tail call optimization. For Python, supporting beginners and amateurs is a higher goal than writing elegant functional code. Even for problems with elegant recursive solutions, beginners seem to find it easier to cobble together a more complicated loop-based solution than to find the simple recursive one. I know that makes everyone really sad :-( and maybe the long-term solution is to fix the school curriculum to teach programming earlier and better, but for now it's reality.

herdrick 18y ago
Good points. But favoring Python lists over recursion is like favoring chocolate over logging. However, I'm probably just playing gotcha here. My apologies to HN and Guido. My more important point is that recursion is good for real world stuff.
- dkarl 17y ago
  Good points. But favoring Python lists over recursion is like favoring chocolate over logging. No, no, it's not at all, not when you approach it from Guido's point of view. To him, the crucial question is, "What's the right way for beginners to process data?" Python and its built-in data structures support iteration and list indexing because that's how beginners do it. Python does not support tail calls because Guido thinks it's a mistake to teach recursion to beginners. I think everyone is misunderstanding Guido's point because they just can't imagine anyone taking his point of view, so they imagine him saying something else. Joe Marshall even called Guido's main points (which he correctly identified, and then ungraciously caricatured) "a sideshow" and said the "true argument" is about the power of recursion. Sorry, Guido doesn't care about the power of recursion, because it isn't valuable to his target programmers, the programmers he wants to serve. He really thinks tail call support would be a very minor feature in Python because it's not important whether you can program in Python that way. He thinks complete stack trace information is very important because it makes things easy and transparent for beginners. That's what's important to Guido and, I would argue, to most Python programmers. When it comes to the future of Python, that's what matters, and Joe Marshall is the sideshow.
  - herdrick 17y ago
    Python's lists are just as good for recursion as Scheme's cons cells - the data structure doesn't really matter. That was my nitpicky point. I agree that Python's emphasis on beginner-friendliness was the smart choice and led, ironically, to its current dominance in numerical computation.

silentbicycle 17y ago

If you want to see a language which is stylistically very similar to Python* , but has TCO, check out Lua. In practice: you can easily add pre-tail-call tracing, you have the option of starting a debugging REPL on error, using iterators is very idiomatic, it makes implementing coroutines and fully-functional closures easier, etc. I happen to think the most significant benefit of TCO is being able to set up "looping" tail calls between multiple functions, but that's just me. * Somewhere between Python and Javascript, specifically.