Expanding the "expression syntax"

[Tagir Valeev]

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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