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Add list slice #706

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Merged
annevk merged 5 commits into from
Apr 14, 2026
Merged

Add list slice #706

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dfe9571
Add slice
jakearchibald Apr 9, 2026
ce2df87
Restore note
jakearchibald Apr 9, 2026
816b8b4
Expand slice algorithm
jakearchibald Apr 10, 2026
5dfaeb9
Handle out of bound values
jakearchibald Apr 10, 2026
f6c8e61
Asserts rather than clamping
jakearchibald Apr 14, 2026
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13 changes: 9 additions & 4 deletions infra.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -1661,10 +1661,15 @@ set of steps on each <a for=list>item</a> in order, use phrasing of the form
"<a for=list>For each</a> |item| of <var ignore>list</var>", and then operate on |item| in the
subsequent prose.

<p>To <dfn export for=list,stack,queue,set>clone</dfn> a <a>list</a> |list| is to create a new
<a>list</a> |clone|, of the same designation, and, <a for=list>for each</a> |item| of |list|,
<a for=list>append</a> |item| to |clone|, so that |clone| <a for=list>contains</a> the same
<a for=list>items</a>, in the same order as |list|.
<p>To <dfn export for=list,stack,queue,set>slice</dfn> a <a>list</a> |list|, with an optional index
<dfn export for=list/slice><var>from</var></dfn> (default 0) and an optional index
<dfn export for=list/slice><var>to</var></dfn> (default |list|'s <a for=list>size</a>), is to create a new
<a>list</a> |slice|, of the same designation, and <a for=list>append</a> each
<a for=list>item</a> of |list|, where the index is greater than or equal to |from| and less than
|to|, to |slice|, maintaining order.
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@annevk annevk Apr 10, 2026

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I think we should make this a list of steps for clarity. That way we can also assert the obvious things about from and to.

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@jakearchibald jakearchibald Apr 10, 2026

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Yeah that's fair.

Are you ok with clone being defined in terms of slice?

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@annevk annevk Apr 10, 2026

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Yeah that seems good. Always nice to have fewer fundamental primitives.

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@jakearchibald jakearchibald Apr 10, 2026

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Done!


<p>To <dfn export for=list,stack,queue,set>clone</dfn> a <a>list</a> |list| is to return a
<a for=list>slice</a> of |list|.

<p class=note>This is a "shallow clone", as the <a for=list>items</a> themselves are not cloned in
any way.
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