Preserve left element types in list subtraction - #15808
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Teach the type system that list subtraction returns a possibly-empty sublist of its left operand while preserving proper-list validation for both operands. Assisted-by: Codex:GPT-5
josevalim
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Aug 29, 2026
| defp remote_apply(:erlang, :--, _info, [left, right], stack) do | ||
| case {list_of(left), list_of(right)} do | ||
| {{_, list_of}, {_, _}} -> | ||
| result = if list_of, do: list(list_of), else: empty_list() |
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@lukaszsamson ideally, we don't want to implement most of those, except for:
In that case, I am thinking the type signature of this would be |
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Actually, ignore me, it is an Erlang function, we need to type it anyway. We may have more precise signatures later, but we do need to type it, so the change is good. I updated my list above. Just check my comment in the code! |
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Teach the type system that list
--returns a possibly empty sublist of its left operand while preserving proper-list validation for both operands.Assisted-by: Codex:GPT-5.6 Sol, Claude Fable 5