d41f39fb10
This PR lets the match compilation procedure use sparse case analysis when the patterns only match on some but not all constructors of an inductive type. This way, less code is produce. Before, code handling each of the other cases was then optimized and commoned-up by later compilation pipeline, but that is wasteful to do. In some cases this will prevent Lean from noticing that a match statement is complete because it performs less case-splitting for the unreachable case. In this case, give explicit patterns to perform the deeper split with `by contradiction` as the right-hand side. At least temporarily, there is also the option to disable this behaviour with ``` set_option backwards.match.sparseCases false ```
38 lines
1.2 KiB
Text
38 lines
1.2 KiB
Text
set_option linter.unusedVariables false
|
||
|
||
/-! A variety of matches that failed at some point during the development of the sparse match features. -/
|
||
|
||
|
||
inductive Finn : Nat → Type where
|
||
| fzero : {n : Nat} → Finn n
|
||
| fsucc : {n : Nat} → Finn n → Finn (n+1)
|
||
|
||
def Finn.min (x : Bool) {n : Nat} (m : Nat) : Finn n → (f : Finn n) → Unit
|
||
| fzero, _ => ()
|
||
| _, fzero => ()
|
||
| fsucc i, fsucc j => ()
|
||
|
||
def boo (x : Fin 3) : Nat :=
|
||
match x with
|
||
| 0 => 1
|
||
| 1 => 2
|
||
| 2 => 4
|
||
|
||
-- This only works if we do not use the sparse cases on when there are no alternatives left
|
||
def List.nth : (as : List α) → (i : Fin as.length) → α
|
||
| a::as, ⟨0, _⟩ => a
|
||
| a::as, ⟨i+1, h⟩ => nth as ⟨i, Nat.lt_of_succ_lt_succ h⟩
|
||
|
||
|
||
-- So does this, taken from the standard library
|
||
example : (a b : Int) → (h : a * b = 0) → a = 0 ∨ b = 0
|
||
| .ofNat 0, _, _ => by simp
|
||
| _, .ofNat 0, _ => by simp
|
||
| .ofNat (a+1), .negSucc b, h => by cases h
|
||
|
||
-- When we use the sparse cases more aggressively, we had to write it like this
|
||
example : (a b : Int) → (h : a * b = 0) → a = 0 ∨ b = 0
|
||
| .ofNat 0, _, _ => by simp
|
||
| _, .ofNat 0, _ => by simp
|
||
| .ofNat (a+1), .negSucc b, h => by cases h
|
||
| .negSucc _, .negSucc _, h => by cases h
|