Expanding the "expression syntax"

[Tagir Valeev]

This is syntactically ambiguous, as there are already initializers with
similar syntax. Also there are code block lambda bodies, so it would
require special parsing rules for lambdas. Using do-expressions is
unambiguous in every context.

On Wed, Apr 5, 2023, 22:34 tom L <tom_L64 at hotmail.com> wrote:

> Hello,
>
>
>
> This sounds like a cool idea, but why use a keyword (do) at the first
> place ?
> I read the discussion, which mostly was about the do keyword, but I feel
> like there shouldn’t be a keyword at the first place.
>
> int foo = {
>
>                 yield 5 ;
>
> }
>
> Blocks already exist, and while they do not return anything currently, you
> could make so if there is a yield, it would mean it can return a value
> basically.
> It’s similar in my opinion to how you can assign the result of a void
> method, but you can from any other return type, except that here it’s
> inferred.
>
> It can also be seen as a generalization of a switch statement.
>
> (Sorry if my vocabulary is off, but I hope you see my point)
>
>
>
> Great regards
>
>
>
> *From : *Tagir Valeev <amaembo at gmail.com>
> *To : *Red IO <redio.development at gmail.com>
> *Cc : *amber-dev <amber-dev at openjdk.org>
> *Object :*Re: Expanding the "expression syntax"
>
>
>
> 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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