49 lines
1.4 KiB
Text
49 lines
1.4 KiB
Text
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/-! # Nested inductive types
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See "Recursion through lists and arrays" in https://blog.lean-lang.org/blog/2024-9-1-lean-4110/
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This test file exercises the `attach`/`unattach` API.
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-/
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namespace List
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inductive Tree where | node : List Tree → Tree
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namespace Tree
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def rev : Tree → Tree
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| node ts => .node (ts.attach.reverse.map (fun ⟨t, _⟩ => t.rev))
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-- Note that `simp` now automatically removes the `attach`.
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@[simp] theorem rev_def (ts : List Tree) :
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Tree.rev (.node ts) = .node (ts.reverse.map rev) := by
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simp [Tree.rev]
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-- Variant with an explicit `have`, rather than using a pattern match.
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def rev' : Tree → Tree
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| node ts => .node (ts.attach.reverse.map (fun t => have := t.2; t.1.rev'))
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@[simp] theorem rev'_def (ts : List Tree) :
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Tree.rev' (.node ts) = .node (ts.reverse.map rev') := by
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simp [Tree.rev']
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/-- Define `size` using a `foldl` over `attach`. -/
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def size : Tree → Nat
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| node ts => 1 + ts.attach.foldl (fun acc ⟨t, _⟩ => acc + t.size) 0
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@[simp] theorem size_def (ts : List Tree) :
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size (.node ts) = 1 + ts.foldl (fun acc t => acc + t.size) 0 := by
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simp [size]
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/-- Define `depth` using a `foldr` over `attach`. -/
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def depth : Tree → Nat
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| node ts => 1 + ts.attach.foldr (fun ⟨t, _⟩ acc => acc + t.depth) 0
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@[simp] theorem depth_def (ts : List Tree) :
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depth (.node ts) = 1 + ts.foldr (fun t acc => acc + t.depth) 0 := by
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simp [depth]
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end Tree
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end List
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