nushell / nushell/nushell.github.io

Are Boolean operators lazy?

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Description

Hello,

TL;DR: Are the and and or Boolean operators guaranteed to be lazy, so we can document it?


I encountered this bug https://github.com/nushell/nushell/issues/10237 which makes last error out on an empty input instead of returning a null if I understand correctly.

So I have written this workaround:

  let filler = if ($text != "") and ($text | split chars | last) == "%" { "%" } else { " " }

This code works without errors for me, so the RHS of the and Boolean operator must not be evaluated / be lazily evaluated.
To put it short, the and operator seems lazy (nu version 0.108.0)

I cannot find it documented in Boolean | Nushell and looking for "lazy" in the documentation does not yield anything related to Booleans.

Is and guaranteed to be lazy in future versions? What about or?
Should we document this behavior?

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked Boolean documentation page and the referenced Nushell issue 10237. Verify whether and and or are guaranteed to evaluate lazily, then document the confirmed behavior and its implications for the shown example on the appropriate Boolean documentation page.

Written by the indexing model from the issue text.

Assessment

Tech stack
shell
Domain
documentation
Issue type
Documentation
Difficulty
2/5
Estimated time
1-3 hours
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
48/100

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