Expanding the "expression syntax"

[Holo The Sage Wolf]

A different approach is to give `yield` the same semantics as `break`, and
interpreting `break label` as `yield label null`, this would make all label
blocks be expressions.

The only thing we need to be careful with is finally block, but this
situation already happens with `return` inside of a finally block, so I
don't think we need to handle this situation differently

On Wed, Apr 5, 2023, 15:55 Tagir Valeev <amaembo at gmail.com> wrote:

> Hello!
>
> Just for the record, three years ago I posted a similar, though more
> universal proposal, "do expressions":
>
> https://mail.openjdk.org/pipermail/amber-spec-experts/2020-March/002046.html
>
> With best regards,
> Tagir Valeev.
>
> On Wed, Apr 5, 2023 at 11:58 AM Red IO <redio.development at gmail.com>
> wrote:
>
>> I did some more research and testing and concluded that loop expressions
>> are more difficult to achieve than I thought and are not as simple as I
>> thought.
>> So I limit my proposal to try expressions since I really think they are
>> worth it.
>> A try expression would follow this syntax:
>> TARGET VARIABLE = TRY_KEYWORD [RECOURSE_BLOCK] TRY_BODY(with every path
>> leading to a yield or throw) [CATCH_BLOCKS(with also a yield or throw in
>> every path)]
>> [FINALLY_BLOCK (with no yield but throw possible)];
>>
>> An example would be:
>> int fileInt = try (var reader = new BufferedReader(new
>> FileReader("test.txt"))) {
>> var line = reader.readLine();
>> if (line == null)
>> yield -1;
>> yield Integer.parseInt(line);
>> } catch (IOException e) {
>> throw new CustomException("Couldn't open file", e);
>> } catch (NumberFormatException e) {
>> yield -1;
>> } finally {
>> if (outsideCondition)
>> throw new CustomCancelledExecption();
>> System.out.println("file read done");
>> };
>>
>> This example is constructed to feature all possible parts of the syntax
>> and is not necessarily code that makes sense to write.
>>
>> Great regards
>> RedIODev
>>
>> On Sat, Mar 4, 2023, 10:55 Red IO <redio.development at gmail.com> wrote:
>>
>>> Currently we have the switch expression as the only expression returning
>>> a result.
>>> Example:
>>> boolean b = switch (1) {
>>> case 0 -> false;
>>> case 1 -> {
>>> yield true;
>>> }
>>> };
>>>
>>> The idea would be to expand this syntax to different expressions for
>>> example the try expression:
>>>
>>> int i = try {
>>> yield Integer.parseInt("Abc");
>>> } catch (NumberFormatException e) {
>>> yield -1;
>>> };
>>>
>>> Or loops:
>>>
>>> String searched = for(String s : args) {
>>> if (s.startsWith("-"))
>>> yield s;
>>> };
>>>
>>> The idea is to make all java control flow expressions able to yield a
>>> value.
>>>
>>> Among many new patterns possible like the examples above it would for
>>> example "clean up" the exception catching initialization:
>>>
>>> Foo foo = null;
>>>
>>> try {
>>> foo = new Foo();
>>> } catch (SomeException e) {
>>> //do something or nothing
>>> } finally {
>>> //maybe change the value again
>>> }
>>>
>>> To
>>>
>>> var foo = try {
>>> yield new Foo();
>>> } catch (SomeException e) {
>>> //throw or yield
>>> } finally {
>>> //throw or do nothing
>>> };
>>>
>>> Another benefit especially in this example is the clearer state of the
>>> result. In an yielding expression you have to either yield or throw. Also
>>> subsequent manipulation in for example the finally block is not possible
>>> making the source of the returned result clear to identify.
>>>
>>> Great regards
>>> RedIODev
>>>
>>
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