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 ```
23 lines
556 B
Text
23 lines
556 B
Text
/--
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trace: [Compiler.saveMono] size: 7
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def foo f x : Option Nat :=
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let _x.1 := f x;
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cases _x.1 : Option Nat
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| Option.some val.2 =>
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let _x.3 := Nat.add val.2 val.2;
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let _x.4 := some ◾ _x.3;
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return _x.4
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| _ =>
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let _x.5 := none ◾;
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return _x.5
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-/
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#guard_msgs in
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set_option trace.Compiler.saveMono true in
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def foo (f : Nat → Option Nat) (x : Nat) : Option Nat :=
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if let some val := f x then
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if let some val2 := f x then
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some <| val + val2
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else
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none
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else
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none
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