feat: deriving instance DecidableEq for Except#1692
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fgdorais merged 3 commits intoleanprover-community:mainfrom Feb 25, 2026
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feat: deriving instance DecidableEq for Except#1692fgdorais merged 3 commits intoleanprover-community:mainfrom
fgdorais merged 3 commits intoleanprover-community:mainfrom
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I was surprised to find out that
Exceptdoesn't have aDecidableEqinstance in Lean, Batteries or Mathlib.I opened a Zulip thread (see #lean4 > No DecidableEq instance for Except?) and was advised to contribute to Batteries or Mathlib. I'm a bit concerned about this being an orphan instance outside the Prelude and about when/if this will make it into upstream though.
Let me know if there's anything else I should take into account.