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[Docs] Clarify the behvior of first, last, and nth on empty generators #3177

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[Docs] Clarify the behvior of first, last, and nth on empty generators #3177

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[Docs] Clarify the behvior of first, last, and nth on empty generators
mousetail Sep 14, 2024
bb8687a
Docs should update for first/1 etc. not /0
mousetail Sep 14, 2024
f5d03dd
"output empty" -> "produce no values"
mousetail Sep 16, 2024
c9d1ce1
Disclaim last being a bug
mousetail Sep 17, 2024
a4e018f
Grammar
mousetail Sep 17, 2024
9b4029b
Update manual.yml
mousetail Sep 17, 2024
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6 changes: 6 additions & 0 deletions docs/content/manual/v1.7/manual.yml
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Expand Up @@ -3017,10 +3017,16 @@ sections:

The `nth(n)` function extracts the nth value of any array at `.`.

`first` and `nth` output `empty` if the generator has insufficient
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I wonder if "produces no output" or "outputs no value" is better then "output empty"? seems to be what is used in other places

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@mousetail mousetail Sep 14, 2024 •
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I found the documentation for try and break also uses the phrase "output/produce empty". In this case I think it's a bit more explicit than "outputs no value".

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@wader wader Sep 16, 2024 •
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Ok, i mostly want consistency but i think i personally prefer "no output" as mentioning empty feel a bit confusing, ex would we document the function empty as producing empty? if we want to use the word empty maybe it should not be written as a function but instad be something like "the empty generator" or "empty output" but then i think i prefer "no output" 🤔

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I have updated the docs to say "produce no values" instead

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@wader wader Sep 16, 2024 •
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👍 let's see what the other maintainers think

But i do wonder what the reasoning was for last/1 to return null?

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One potential "fixed" last that outputs no values for an empty generator would be this:

def last(g): reduce g as $item ([0,null]; [first+1,$item])|if first>0 then last else empty end;

A lot less elagent than the current implementation though.

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See #1869. This is a bug that should be fixed in the future.

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@itchyny 👍 oh long discussion, seems fascinatingly messy :)

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That branch is 5 years old, I doubt it will still be merged

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It's better to use byte code to avoid boxing like the PR even if it makes more messy.

elements. `last` returns `null` instead.

examples:
- program: "[range(.)]|[first, last, nth(5)]"
input: "10"
output: ["[0,9,5]"]
- program: "[range(.)]|[[first], [last], [nth(5)]]"
input: "0"
output: ["[[],[null],[]]"]

- title: "`reduce`"
body: |
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