[e-lang] easy-when-binds-return

[Thomas Leonard]

People often try to use return inside when blocks. Currently, this just
produces confusing "Ejector must be enabled" errors.

How about requiring the use of "return" to return a value from a when block?

There are a few places where this would be useful:

- Often you will move a whole block in to or out of a when() block. It's
useful if you don't have to change all return lines when you do this.

- People sometimes don't notice that the value of the last expression is
used, and put something after it.

e.g. they change

return when (foo) -> {
foo.invoke()
}

to

return when (foo) -> {
foo.invoke()
traceln("here")
}

and then wonder why they're getting null pointer exceptions elsewhere.

- You can accidentally return a value, when all you intended was to tell
the caller when you were done.


Patch to add #pragma.enable("easy-when-binds-return"):

http://gitorious.org/~tal-itinnov/repo-roscidus/it-innovation/commit/c10e7bc99bbfbabbbb28ea714e19855fbca8c389
--
Dr Thomas Leonard
IT Innovation Centre
Gamma House, Enterprise Road,
Southampton SO16 7NS, UK


tel: [phone]

mailto:***@it-innovation.soton.ac.uk
http://www.it-innovation.soton.ac.uk/

[Kevin Reid]

Post by Thomas Leonard
People often try to use return inside when blocks. Currently, this just
produces confusing "Ejector must be enabled" errors.
How about requiring the use of "return" to return a value from a when block?

No.

We used to do that (along with otherwise treating the when-block more like a function), and decided it was too heavyweight and confusing. This makes 'when' more like other control structures. In particular, it is more like the user-defined control structures of the "lambda-args" pragma; we *expect* to find more "eventual control structures" to want.

I will not support any change to 'when' which moves it farther from the semantics expressible by lambda-args.

I am also against making E more 'imperative style' given that it's not going to stop being a hybrid.