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0 pointsptx6y ago0 comments

What would "do/while" look like in Python? Since blocks don't have end markers (e.g. "end", "}", etc.) there's nowhere to put the while expression if you want the syntax to be consistent with the rest of the language.

0 comments

ben5096y ago

One solution would be to borrow from Perl. You make a do block that executes once unless continued, and allow conditions on break and continue:

    do:
        thing()
        thing()
        continue if condition

And you can now express "skip ahead" with a `break if X` as well.

adrianratnapala6y ago

Yes, although you don't have to be so perlish as to do the if in that order

    do:
        thing()
        thing()
        if condition:
            continue

nerdponx6y ago

I envisioned it like "if/else" or "for/else" or "while/else", where a "do" block must be followed by a "while" block.

    x = 0
    do:
        x += 1
    while:
        x < 10

toxik6y ago

This completely contradicts the rest of Python grammar, and indeed many languages’ grammars. The consistent way would then be `while x < 10` but that too looks ridiculous. The issue is that you can’t have post-clause syntax in Python due to its infamous spacing-is-syntax idea.

ben5096y ago

I'm not sure why the consistent way looks ridiculous.

    do:
        body()
        body()
    while x < 10

It's just a compound statement consumes the trailing while clause.

Decorators already precede a function (or class) definition[2], and one alternative for the ill-fated switch statement[1] was to have switch precede the case blocks to avoid excessive indentation.

So there's plenty of precedent in the other direction.

[1]: https://www.python.org/dev/peps/pep-3103/#alternative-3

[2]: https://docs.python.org/3/reference/grammar.html

1 more reply

mkl6y ago

Of course you can have post-clause syntax: if...else, try...except, for...else, etc.

(Edit: Actually, I think I know what you were saying now, and those aren't quite the same thing as they need a line after them.)

I do think the condition on the next line isn't the way to do solve this problem though (and I don't think it needs solving, while True: ... if ...: break does the job).

krferriter6y ago

Why does `while x < 10` look ridiculous? It looks exactly like the syntax for regular while loops, just in this case it's after a `do:` block. And the example above yours looks like try/catch syntax, but tbh I like the one you suggested a bit more.

nerdponx6y ago

You're right, it would be pretty weird to rely on implicitly "returning" a value from an expression like that.

But I don't think having it all on one line would be that bad.

j / k navigate · click thread line to collapse

0 comments

ben5096y ago

One solution would be to borrow from Perl. You make a do block that executes once unless continued, and allow conditions on break and continue:

    do:
        thing()
        thing()
        continue if condition

And you can now express "skip ahead" with a `break if X` as well.

adrianratnapala6y ago

Yes, although you don't have to be so perlish as to do the if in that order

    do:
        thing()
        thing()
        if condition:
            continue

nerdponx6y ago

I envisioned it like "if/else" or "for/else" or "while/else", where a "do" block must be followed by a "while" block.

    x = 0
    do:
        x += 1
    while:
        x < 10

toxik6y ago

ben5096y ago

I'm not sure why the consistent way looks ridiculous.

    do:
        body()
        body()
    while x < 10

It's just a compound statement consumes the trailing while clause.

Decorators already precede a function (or class) definition[2], and one alternative for the ill-fated switch statement[1] was to have switch precede the case blocks to avoid excessive indentation.

So there's plenty of precedent in the other direction.

[1]: https://www.python.org/dev/peps/pep-3103/#alternative-3

[2]: https://docs.python.org/3/reference/grammar.html

1 more reply

mkl6y ago

Of course you can have post-clause syntax: if...else, try...except, for...else, etc.

(Edit: Actually, I think I know what you were saying now, and those aren't quite the same thing as they need a line after them.)

I do think the condition on the next line isn't the way to do solve this problem though (and I don't think it needs solving, while True: ... if ...: break does the job).

krferriter6y ago

nerdponx6y ago

You're right, it would be pretty weird to rely on implicitly "returning" a value from an expression like that.

But I don't think having it all on one line would be that bad.

j / k navigate · click thread line to collapse