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refactor: deriving DecidableEq to use termination_by structural #4826

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Jul 29, 2024
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refactor: deriving DecidableEq to use termination_by structural #4826

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3ef3e88
refactor: deriving DecidableEq to use `termination_by structural`
nomeata Jul 25, 2024
1f3061a
Only for recursive data types
nomeata Jul 25, 2024
e6b1702
Merge branch 'nightly-with-mathlib' of github.com:leanprover/lean4 in…
nomeata Jul 29, 2024
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10 changes: 8 additions & 2 deletions src/Lean/Elab/Deriving/DecEq.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -91,8 +91,14 @@ def mkAuxFunction (ctx : Context) (auxFunName : Name) (indVal : InductiveVal): T
let header ← mkDecEqHeader indVal
let body ← mkMatch ctx header indVal
let binders := header.binders
let type ← `(Decidable ($(mkIdent header.targetNames[0]!) = $(mkIdent header.targetNames[1]!)))
`(private def $(mkIdent auxFunName):ident $binders:bracketedBinder* : $type:term := $body:term)
let target₁ := mkIdent header.targetNames[0]!
let target₂ := mkIdent header.targetNames[1]!
let termSuffix ← if indVal.isRec
then `(Parser.Termination.suffix|termination_by structural $target₁)
else `(Parser.Termination.suffix|)
let type ← `(Decidable ($target₁ = $target₂))
`(private def $(mkIdent auxFunName):ident $binders:bracketedBinder* : $type:term := $body:term
$termSuffix:suffix)

def mkAuxFunctions (ctx : Context) : TermElabM (TSyntax `command) := do
let mut res : Array (TSyntax `command) := #[]
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5 changes: 5 additions & 0 deletions tests/lean/decEqMutualInductives.lean.expected.out
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
let inst✝ := decEqListTree✝ @a✝ @b✝;
if h✝ : @a✝ = @b✝ then by subst h✝; exact isTrue✝ rfl✝
else isFalse✝ (by intro n✝; injection n✝; apply h✝ _; assumption)
termination_by structural x✝
private def decEqListTree✝ (x✝² : @ListTree✝) (x✝³ : @ListTree✝) : Decidable✝ (x✝² = x✝³) :=
match x✝², x✝³ with
| @ListTree.nil, @ListTree.nil => isTrue✝¹ rfl✝¹
Expand All @@ -19,6 +20,7 @@
if h✝³ : @a✝² = @b✝² then by subst h✝³; exact isTrue✝² rfl✝²
else isFalse✝² (by intro n✝¹; injection n✝¹; apply h✝³ _; assumption)
else isFalse✝³ (by intro n✝²; injection n✝²; apply h✝² _; assumption)
termination_by structural x✝²
end,
instance : DecidableEq✝ (@ListTree✝) :=
decEqListTree✝]
Expand All @@ -33,18 +35,21 @@
let inst✝ := decEqFoo₂✝ @a✝ @b✝;
if h✝¹ : @a✝ = @b✝ then by subst h✝¹; exact isTrue✝¹ rfl✝¹
else isFalse✝¹ (by intro n✝; injection n✝; apply h✝¹ _; assumption)
termination_by structural x✝
private def decEqFoo₂✝ (x✝² : @Foo₂✝) (x✝³ : @Foo₂✝) : Decidable✝ (x✝² = x✝³) :=
match x✝², x✝³ with
| @Foo₂.foo₂ a✝¹, @Foo₂.foo₂ b✝¹ =>
let inst✝¹ := decEqFoo₃✝ @a✝¹ @b✝¹;
if h✝² : @a✝¹ = @b✝¹ then by subst h✝²; exact isTrue✝² rfl✝²
else isFalse✝² (by intro n✝¹; injection n✝¹; apply h✝² _; assumption)
termination_by structural x✝²
private def decEqFoo₃✝ (x✝⁴ : @Foo₃✝) (x✝⁵ : @Foo₃✝) : Decidable✝ (x✝⁴ = x✝⁵) :=
match x✝⁴, x✝⁵ with
| @Foo₃.foo₃ a✝², @Foo₃.foo₃ b✝² =>
let inst✝² := decEqFoo₁✝ @a✝² @b✝²;
if h✝³ : @a✝² = @b✝² then by subst h✝³; exact isTrue✝³ rfl✝³
else isFalse✝³ (by intro n✝²; injection n✝²; apply h✝³ _; assumption)
termination_by structural x✝⁴
end,
instance : DecidableEq✝ (@Foo₁✝) :=
decEqFoo₁✝]
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