25 lines
764 B
Text
25 lines
764 B
Text
theorem modifySize {A : Type u} (as : Array A) (f : A → A) (n : Nat) : (as.modify n f).size = as.size := by
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simp [Array.modify, Array.modifyM, Id.run]; split <;> simp [Id.run]
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structure Idx (p : Array String) where
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n : Fin p.size
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structure Store where
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arr : Array String
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-- integer pointers into `arr`, type-indexed by `arr`
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ids : Array (Idx arr)
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instance {arr : Array String} {f : String → String} {n : Nat} : Coe (Array (Idx arr)) (Array (Idx (arr.modify n f))) where
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coe xs :=
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xs.map (fun x => Idx.mk ((modifySize arr f n) ▸ x.n))
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def store1 : Store := {
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arr := #["a", "b", "c", "d", "e"]
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ids := #[⟨2, by simp⟩]
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}
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def tryCoeStore := {
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store1 with
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-- using a lambda here hangs
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arr := store1.arr.modify 2 (fun _ => "Z")
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}
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