58 lines
1.4 KiB
Text
58 lines
1.4 KiB
Text
structure ListZipper (α : Type) :=
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(xs : List α) (bs : List α)
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-- set_option trace.compiler.ir.rc true
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variables {α : Type}
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namespace ListZipper
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def goForward : ListZipper α → ListZipper α
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| ⟨[], bs⟩ => ⟨[], bs⟩
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| ⟨x::xs, bs⟩ => ⟨xs, x::bs⟩
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def goBackward : ListZipper α → ListZipper α
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| ⟨xs, []⟩ => ⟨xs, []⟩
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| ⟨xs, b::bs⟩ => ⟨b::xs, bs⟩
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def insert : ListZipper α → α → ListZipper α
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| ⟨xs, bs⟩, x => ⟨xs, x::bs⟩
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def erase : ListZipper α → ListZipper α
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| ⟨[], bs⟩ => ⟨[], bs⟩
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| ⟨x::xs, bs⟩ => ⟨xs, bs⟩
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def curr [Inhabited α] : ListZipper α → α
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| ⟨[], bs⟩ => arbitrary _
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| ⟨x::xs, bs⟩ => x
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def currOpt : ListZipper α → Option α
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| ⟨[], bs⟩ => none
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| ⟨x::xs, bs⟩ => some x
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def toList : ListZipper α → List α
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| ⟨xs, bs⟩ => bs.reverse ++ xs
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def atEnd (z : ListZipper α) : Bool :=
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z.xs.isEmpty
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end ListZipper
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def List.toListZipper (xs : List α) : ListZipper α :=
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⟨xs, []⟩
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partial def testAux : ListZipper Nat → ListZipper Nat
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| z =>
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if z.atEnd then
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z
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else if z.curr % 2 == 0 then
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testAux (z.goForward.insert 0)
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else if z.curr > 20 then
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testAux z.erase
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else
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testAux z.goForward
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def test (xs : List Nat) : List Nat :=
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(testAux xs.toListZipper).toList
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#eval (IO.println (test [10, 11, 13, 20, 22, 40, 41, 11]) : IO Unit)
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