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Editorial Team
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Asked: 2026-05-15T07:47:35+00:00

In another question, I saw the following syntax: #[unset!] What is that? If I

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In another question, I saw the following syntax:

#[unset!]

What is that? If I say type? #[unset!] in R3, it tells me unset!, but it doesn’t solve the mystery of what #[] is.

So curious.

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1 Answer

  1. Editorial Team

    Looks like it’s the value-construction syntax for an unset instance, as opposed to the word unset!:

    >> comparison: [unset! #[unset!]]
== [unset! unset!]

>> type? first comparison
== word!

>> type? second comparison
== unset!

>> second comparison
>> first comparison
== unset!

    If you’re in a programmatic context you could do this with to-unset, but having a literal notation lets you dodge the reduce:

    >> comparison: reduce ['unset! to-unset none]
== [unset! unset!]

>> second comparison
>> first comparison
== unset!

    Looks like they’ve reserved the #[…] syntax for more of these kinds of constructors.

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