Lean 4 fork for HoTT-compatible kernel extensions (Path types, transport, HITs). Maintained against upstream leanprover/lean4.
c0f264ffe0
`Array.set!` and `Array.swap!` are fairly similar operations, both modify an array, both take an index that it out of bounds. But they behave different; all of these return `true` ``` #eval #[1,2].set! 2 42 == #[1,2] -- with panic #reduce #[1,2].set! 2 42 == #[1,2] -- no panic #eval #[1,2].swap! 0 2 == #[1,2] -- with panic #reduce #[1,2].swap! 0 2 == default -- no panic ``` The implementations are ``` @[extern "lean_array_set"] def Array.set! (a : Array α) (i : @& Nat) (v : α) : Array α := Array.setD a i v ``` but ``` @[extern "lean_array_swap"] def swap! (a : Array α) (i j : @& Nat) : Array α := if h₁ : i < a.size then if h₂ : j < a.size then swap a ⟨i, h₁⟩ ⟨j, h₂⟩ else panic! "index out of bounds" else panic! "index out of bounds" ``` It seems to be more consistent to unify the behaviors, and define ``` @[extern "lean_array_swap"] def swap! (a : Array α) (i j : @& Nat) : Array α := if h₁ : i < a.size then if h₂ : j < a.size then swap a ⟨i, h₁⟩ ⟨j, h₂⟩ else a else a ``` Also adds docstrings. Fixes #3196 |
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This is the repository for Lean 4.
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