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chore: turn off Inhabited (Sum α β) instances #5284

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merged 4 commits into from
Sep 9, 2024
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chore: turn off Inhabited (Sum α β) instances #5284

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cdbd3d6
chore: turn off [Inhabited β] : Inhabited (Sum α β)
kim-em Sep 6, 2024
25eb95c
make reducible
kim-em Sep 6, 2024
eae6349
chore: turn off Inhabited (Sum α β) instances
kim-em Sep 8, 2024
9057084
add nonempty instances
kim-em Sep 8, 2024
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30 changes: 26 additions & 4 deletions src/Init/Core.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -165,9 +165,23 @@ inductive PSum (α : Sort u) (β : Sort v) where

@[inherit_doc] infixr:30 " ⊕' " => PSum

instance {α β} [Inhabited α] : Inhabited (PSum α β) := ⟨PSum.inl default⟩
/--
`PSum α β` is inhabited if `α` is inhabited.
This is not an instance to avoid non-canonical instances.
-/
@[reducible] def PSum.inhabitedLeft {α β} [Inhabited α] : Inhabited (PSum α β) := ⟨PSum.inl default⟩

/--
`PSum α β` is inhabited if `β` is inhabited.
This is not an instance to avoid non-canonical instances.
-/
@[reducible] def PSum.inhabitedRight {α β} [Inhabited β] : Inhabited (PSum α β) := ⟨PSum.inr default⟩

instance PSum.nonemptyLeft [h : Nonempty α] : Nonempty (PSum α β) :=
Nonempty.elim h (fun a => ⟨PSum.inl a⟩)

instance {α β} [Inhabited β] : Inhabited (PSum α β) := ⟨PSum.inr default⟩
instance PSum.nonemptyRight [h : Nonempty β] : Nonempty (PSum α β) :=
Nonempty.elim h (fun b => ⟨PSum.inr b⟩)

/--
`Sigma β`, also denoted `Σ a : α, β a` or `(a : α) × β a`, is the type of dependent pairs
Expand Down Expand Up @@ -1150,12 +1164,20 @@ end Subtype
section
variable {α : Type u} {β : Type v}

instance Sum.inhabitedLeft [Inhabited α] : Inhabited (Sum α β) where
/-- This is not an instance to avoid non-canonical instances. -/
@[reducible] def Sum.inhabitedLeft [Inhabited α] : Inhabited (Sum α β) where
default := Sum.inl default

instance Sum.inhabitedRight [Inhabited β] : Inhabited (Sum α β) where
/-- This is not an instance to avoid non-canonical instances. -/
@[reducible] def Sum.inhabitedRight [Inhabited β] : Inhabited (Sum α β) where
default := Sum.inr default

instance Sum.nonemptyLeft [h : Nonempty α] : Nonempty (Sum α β) :=
Nonempty.elim h (fun a => ⟨Sum.inl a⟩)

instance Sum.nonemptyRight [h : Nonempty β] : Nonempty (Sum α β) :=
Nonempty.elim h (fun b => ⟨Sum.inr b⟩)

instance {α : Type u} {β : Type v} [DecidableEq α] [DecidableEq β] : DecidableEq (Sum α β) := fun a b =>
match a, b with
| Sum.inl a, Sum.inl b =>
Expand Down
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