6 ms·

I love Rust, I just wish it could get rid of semicolons. Quite a lot of discussions around this.

kthxb 6y ago
of all the complaints to have...
Tade0 6y ago
Any such move will eventually result in automatic semicolon insertion in some shape or form. What's wrong with semicolons anyway?
- matesz 6y ago
  Nothing wrong with semicolons. IMO they make code look a little bit less readable - you need to look at semicolon while you could be just looking at the empty line. One of the reasons people like python.
  - colejohnson66 6y ago
    This is a valid point. Without the context, the “everything is an expression” forces one to look for a line without a semicolon to see the expression result. In a 5 line function, that’s easy, but in a nested match, it can be hard.
    - unanswered 6y ago
      It can only possibly be at the end, so it's not really hard?
deetsb 6y ago
I wasn't a fan at first (coming from Python), but I really like that it allows you to make expressions into statements (I'm sure there's more going on then just that, but it was pretty cool to see that if/match are generally expressions but if I don't want them to be, ";" can change that!).
colejohnson66 6y ago
I’d like that too, but: if you get rid of semicolons, how do you avoid something like JavaScript’s automatic semicolon insertion mess? For example: return x; turns into: return; x; which is clearly not what was intended. Sure, if Rust copied JavaScript’s algorithm, the compiler would throw a type error (where () is not compatible with typeof(x)) and complain of dead code instead of silently failing, but it seems like a hard task. Then again, I’m not a compiler writer.
- bcoates 6y ago
  Python's solution to this is that a randomly indented block is an error. Many languages restrict statement-expressions to function calls and other expressions with explicit side-effects. Another choice would be to avoid syntax where you can optionally append expressions to an otherwise complete statement (so only one of "return" and "return expr" are allowed, and the other has an alternate spelling) Or the parser could forbid line continuation in the absence of a trailing binary operator, which makes mid-statement newlines illegal outside of a highly visible special case so users would be trained out of inserting them at random before they introduced errors. Both JavaScript and python do something like the last one but both screw it up; JavaScript also allows leading operators and open-brackets to continue the previous line which is a huge mess, and python uses brackets to continue lines but parens are both optional around most expressions and overloaded (generators, tuples). If you wanted to go that way you would need a bracket that meant "this is syntactically a single expression and has no other meaning"
  - zozbot234 6y ago
    The easiest solution might be to simply allow \ as a line-continuation operator. So you'd write: return \ x;
    - colejohnson66 6y ago
      But then you’ve just swapped one set of trade offs for another. It seems like a weak solution. IIRC semicolons were added to the languages of old to avoid the need for line continuation marks.
paavohtl 6y ago
As far as I know, a (C-like) language must either have: - A statement separator (semicolons) - Significant whitespace Otherwise parsing the language is very likely ambiguous, e.g JavaScript [1] [2]. [1] https://flaviocopes.com/javascript-automatic-semicolon-insertion/ https://flaviocopes.com/javascript-automatic-semicolon-inser... [2] https://medium.com/better-programming/you-might-need-those-semicolons-in-your-javascript-after-all-b28154f93ea8 https://medium.com/better-programming/you-might-need-those-s...
- hu3 6y ago
  Go doesn't have either: https://play.golang.org/ https://play.golang.org/
  - paavohtl 6y ago
    Ah, but it does. Statements are separated by newlines. That is the same as significant whitespace (or a statement separator; you can interpret it either way).
    - hu3 6y ago
      Technically correct. But the point is about ergonomy. Go doesn't require semicolons neither indentation. That coupled with gofmt auto-formatter makes coding more pleasant.
- duckerude 6y ago
  JavaScript messed it up, but Python did it well. A newline is a statement separator, unless it's e.g. between parentheses where a statement separator wouldn't make sense. Unlike JavaScript, that means you don't have to look at the next line to figure out whether the statement continues. JavaScript assumes a newline doesn't end a statement, until proven otherwise. Python assumes it does end a statement unless it very clearly can't. It's independent from Python's other significant whitespace, so you could use it in a more "C-like" syntax. But it wouldn't be a good fit for Rust. In Rust, leaving the semicolon off the final statement in a block already changes its meaning, so that would become ambiguous. It also uses method chaining syntax a great deal more than Python, which is a bit awkward because you have to wrap the expression in parentheses (though autoformatting helps). And of course it would break most existing code.

of all the complaints to have...

Any such move will eventually result in automatic semicolon insertion in some shape or form. What's wrong with semicolons anyway?

matesz 6y ago
Nothing wrong with semicolons. IMO they make code look a little bit less readable - you need to look at semicolon while you could be just looking at the empty line. One of the reasons people like python.
- colejohnson66 6y ago
  This is a valid point. Without the context, the “everything is an expression” forces one to look for a line without a semicolon to see the expression result. In a 5 line function, that’s easy, but in a nested match, it can be hard.
  - unanswered 6y ago
    It can only possibly be at the end, so it's not really hard?

deetsb 6y ago

I wasn't a fan at first (coming from Python), but I really like that it allows you to make expressions into statements (I'm sure there's more going on then just that, but it was pretty cool to see that if/match are generally expressions but if I don't want them to be, ";" can change that!).

colejohnson66 6y ago

I’d like that too, but: if you get rid of semicolons, how do you avoid something like JavaScript’s automatic semicolon insertion mess? For example: return x; turns into: return; x; which is clearly not what was intended. Sure, if Rust copied JavaScript’s algorithm, the compiler would throw a type error (where () is not compatible with typeof(x)) and complain of dead code instead of silently failing, but it seems like a hard task. Then again, I’m not a compiler writer.

bcoates 6y ago
Python's solution to this is that a randomly indented block is an error. Many languages restrict statement-expressions to function calls and other expressions with explicit side-effects. Another choice would be to avoid syntax where you can optionally append expressions to an otherwise complete statement (so only one of "return" and "return expr" are allowed, and the other has an alternate spelling) Or the parser could forbid line continuation in the absence of a trailing binary operator, which makes mid-statement newlines illegal outside of a highly visible special case so users would be trained out of inserting them at random before they introduced errors. Both JavaScript and python do something like the last one but both screw it up; JavaScript also allows leading operators and open-brackets to continue the previous line which is a huge mess, and python uses brackets to continue lines but parens are both optional around most expressions and overloaded (generators, tuples). If you wanted to go that way you would need a bracket that meant "this is syntactically a single expression and has no other meaning"
- zozbot234 6y ago
  The easiest solution might be to simply allow \ as a line-continuation operator. So you'd write: return \ x;
  - colejohnson66 6y ago
    But then you’ve just swapped one set of trade offs for another. It seems like a weak solution. IIRC semicolons were added to the languages of old to avoid the need for line continuation marks.

paavohtl 6y ago

As far as I know, a (C-like) language must either have: - A statement separator (semicolons) - Significant whitespace Otherwise parsing the language is very likely ambiguous, e.g JavaScript [1] [2]. [1] https://flaviocopes.com/javascript-automatic-semicolon-insertion/ https://flaviocopes.com/javascript-automatic-semicolon-inser... [2] https://medium.com/better-programming/you-might-need-those-semicolons-in-your-javascript-after-all-b28154f93ea8 https://medium.com/better-programming/you-might-need-those-s...

hu3 6y ago
Go doesn't have either: https://play.golang.org/ https://play.golang.org/
- paavohtl 6y ago
  Ah, but it does. Statements are separated by newlines. That is the same as significant whitespace (or a statement separator; you can interpret it either way).
  - hu3 6y ago
    Technically correct. But the point is about ergonomy. Go doesn't require semicolons neither indentation. That coupled with gofmt auto-formatter makes coding more pleasant.
duckerude 6y ago
JavaScript messed it up, but Python did it well. A newline is a statement separator, unless it's e.g. between parentheses where a statement separator wouldn't make sense. Unlike JavaScript, that means you don't have to look at the next line to figure out whether the statement continues. JavaScript assumes a newline doesn't end a statement, until proven otherwise. Python assumes it does end a statement unless it very clearly can't. It's independent from Python's other significant whitespace, so you could use it in a more "C-like" syntax. But it wouldn't be a good fit for Rust. In Rust, leaving the semicolon off the final statement in a block already changes its meaning, so that would become ambiguous. It also uses method chaining syntax a great deal more than Python, which is a bit awkward because you have to wrap the expression in parentheses (though autoformatting helps). And of course it would break most existing code.