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What should an empty block evaluate to? #36

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ltratt opened this issue May 31, 2020 · 3 comments
Open

What should an empty block evaluate to? #36

ltratt opened this issue May 31, 2020 · 3 comments
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language design This issue requires design decisions spec Needs specification, or is specification related.

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@ltratt
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ltratt commented May 31, 2020

What should this program print?

empty_block = (
    run = (
        [] value println.
    )
)

Java SOM prints "instance of Block1". There's nothing wrong with that per se, but it wasn't what I was expecting because a) (at least as far as I know) blocks can't get access to their instances under normal circumstances b) methods return self unless otherwise specified. I wondered if this was intentional or not? I couldn't find any obvious clues in Java SOM's source to indicate anything either way.
@smarr smarr added language design This issue requires design decisions spec Needs specification, or is specification related. labels May 31, 2020
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smarr commented May 31, 2020

Hmpf. You're too good at this...

The answer should really be nil, following all other Smalltalks I tested.

Blocks return the value of their last expression. Since there was no expression, there's no value.
At least that would be my interpretation of what the other Smalltalks do (GNU Smalltalk, Amber Smalltalk, Squeak 2, 5, and Pharo).

@ltratt
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ltratt commented May 31, 2020

My main skill here is ignorance! nil was what I was vaguely expecting, and it's easy to implement, so I won't complain!

@ltratt ltratt mentioned this issue May 31, 2020
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bors bot added a commit to softdevteam/yksom that referenced this issue Jun 1, 2020
@bors @ltratt
Merge #128
5b25779 
128: Empty blocks evaluate to nil. r=ptersilie a=ltratt

Whilst here, it is silly for `add_global` to take a `String` when both callers have to call `to_owned` for the `&str` they really have.

Note this is different behaviour from (at least) Java SOM (see SOM-st/SOM#36).

Co-authored-by: Laurence Tratt <[email protected]>
This was referenced Aug 24, 2020
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smarr commented Aug 24, 2020

Adding tests with #54

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