26ad4d6972
This PR extracts the functional (lambda) passed to `brecOn` in structural recursion into a named `_f` helper definition (e.g. `foo._f`), similar to how well-founded recursion uses `._unary`. This way the functional shows up with a helpful name in kernel diagnostics rather than as an anonymous lambda. The `_f` definition is added with `.abbrev` kernel reducibility hints and the `@[reducible]` elaborator attribute, so the kernel unfolds it eagerly after `brecOn` iota-reduces. For inductive predicates, the previous inline lambda behavior is kept. To ensure that parent definitions still get the correct reducibility height (since `getMaxHeight` ignores `.abbrev` definitions), each `_f`'s body height is registered via a new `defHeightOverrideExt` environment extension. `getMaxHeight` checks this extension for all definitions, making the height computation transparent to the extraction. This change improves code size (a bit). It may regress kernel reduction times, especially if a function defined by structural recursion is used in kernel reduction proofs on the hot path. Functions defined by structural recursion are not particularly fast to reduce anyways (due to the `.brecOn` construction), so already now it may be worth writing a kernel-reduction-friendly function manually (using the recursor directly, avoiding overloaded operations). This change will guide you in knowing which function to optimize. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
77 lines
2.2 KiB
Text
77 lines
2.2 KiB
Text
-- Test that structural recursion creates a named `_f` helper definition
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-- for the functional passed to `brecOn`.
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-- Simple case: single function
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def addAdjacent : List Nat → List Nat
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| [] => []
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| [a] => [a]
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| a::b::as => (a+b) :: addAdjacent as
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-- The `_f` helper should exist in the environment
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/-- info: addAdjacent._f : (x : List Nat) → List.below x → List Nat -/
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#guard_msgs in #check @addAdjacent._f
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-- Verify computation still works
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/-- info: [3, 7] -/
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#guard_msgs in #eval addAdjacent [1, 2, 3, 4]
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-- Mutual recursion: each function gets its own `_f`
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mutual
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def even : Nat → Bool
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| 0 => true
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| n + 1 => odd n
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def odd : Nat → Bool
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| 0 => false
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| n + 1 => even n
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end
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/-- info: even._f : (x : Nat) → Nat.below x → Bool -/
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#guard_msgs in #check @even._f
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/-- info: odd._f : (x : Nat) → Nat.below x → Bool -/
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#guard_msgs in #check @odd._f
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/-- info: true -/
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#guard_msgs in #eval even 4
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/-- info: true -/
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#guard_msgs in #eval odd 3
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-- With fixed parameters
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def myMap (f : α → β) : List α → List β
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| [] => []
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| x::xs => f x :: myMap f xs
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/-- info: @myMap._f : {α : Type u_1} → {β : Type u_2} → (α → β) → (x : List α) → List.below x → List β -/
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#guard_msgs in #check @myMap._f
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-- The `_f` helper shows up with a helpful name in kernel diagnostics
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def fib (n : Nat) :=
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match n with
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| 0 | 1 => 1
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| x+2 => fib x + fib (x+1)
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termination_by structural n
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/--
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trace: [diag] Diagnostics
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[reduction] unfolded declarations (max: 79, num: 4):
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[reduction] Nat.rec ↦ 79
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[reduction] Add.add ↦ 41
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[reduction] HAdd.hAdd ↦ 41
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[reduction] fib ↦ 40
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[reduction] unfolded reducible declarations (max: 79, num: 1):
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[reduction] Nat.casesOn ↦ 79
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[kernel] unfolded declarations (max: 80, num: 6):
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[kernel] Nat.rec ↦ 80
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[kernel] Nat.casesOn ↦ 77
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[kernel] fib._f ↦ 39
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[kernel] fib.match_1 ↦ 39
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[kernel] Add.add ↦ 36
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[kernel] HAdd.hAdd ↦ 36
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use `set_option diagnostics.threshold <num>` to control threshold for reporting counters
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-/
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#guard_msgs in
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set_option diagnostics true in
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set_option diagnostics.threshold 10 in
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theorem fib_20 : fib 20 = 10946 := rfl
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