Branching or Exit Points : Quad Saga

[genieme]

Branching or Exit Points : Quad Saga

• Consistency : promotes simplicity
• Simplicity : promotes easy learning.

Names for the 4 functions :

• fn branchOut() returns ()
• fn branchTo(Label) returns ()
• fn branchWith() returns Val
• fn branchIf(BoolExp) returns ()

Syntaxes of the 4 Expressions :

• break; or break ();
• break 'label;
• break val;
• break if x > y; ?

we need ‘break if’ expression.

‘if’ is the filter for the exit point : exit iff true.

Usage : inside ‘loop’ block

loop {

break if x > y;

// equivalent to js : while (x > y) {… }

… }

loop { …

// equivalent to js : do{ … } while (x > y);

break if x > y; }

loop { …

// see ada-lang : ‘exit when’ syntax for an equivalent. // 2 or more can be placed anywhere in the the loop, scattered or not.

break if x > y;

… }

Note : that is a lot of flexibility and expressive powess. Yet the rust core team keeps it from us ??

Please correct the wrong ??

when teaching the branching concept to school students, leaving one component out is a disservice. they need complete understanding and practice of the concept.

Please Help Us Out. THANKS.

[dtolnay]

What are some reasons to prefer break if x > y over if x > y { break }?

[genieme]

@dtolnay the ‘if’ keyword is being used as a filter.

we can get rid of if statement or expression, if need be

we can get rid of while(){} statement or expression also

I am trying to promote consistency, which may lower the learning

curve barrier: ‘On Boarding’.

And use match or loop expression or statement instead.

less syntax -> less to learn

[Diggsey]

the ‘if’ keyword is being used as a filter.

that is a very arbitrary distinction to make, there’s no real difference between the two constructs - you seem to be suggesting that the design of the AST is important for a beginner to the language. Are you sure you’re not just arguing for this syntax because it reads more like natural language?

less syntax -> less to learn

So how does adding more redundant syntax help?

[dtolnay]

To clarify, in your code is the behavior identical to if x > y { break }?

[genieme]

@dtolnay and @Diggsey

I am discussing the break exit points as a set of four entities.

they are all related to the same concept : exit points.

that is the consistency.

‘break if’ is the last one remaining.

Yes its semaintics is equivalent to : if (x>y) {break;}

but that is not an exit-point or branching.

• break;
• break 5;
• break 'label;
• break if x > y;

CONSISTENCY

I personally do not use the while keyword.

it is conditional repetition. and not that flexible at all.

‘loop’ keyword + ‘break if’ combine give great flexibility.

see the many ways of using them in the original post.

we can deprecate ‘while’ and ‘if’ statement altogether.

one syntax in : two syntax out

[ExpHP]

we can deprecate ‘while’ and ‘if’ statement altogether.

While we’re at it, we can deprecate for loops and block expressions too. And we can also get rid of bare break; best be explicit with break if true:

// old rust
let sorted = {
    let mut vec: Vec<_> = iter.collect();
    vec.sort();
    vec
};

// new, idiomatic rust
let sorted = loop {
    let mut vec: Vec<_> = iter.collect();
    vec.sort();
    break vec if true;
};

[system]

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