e9d85f49e6
Based on the discussion at https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/for.2C.20unexpected.20need.20for.20type.20ascription/near/269083574 The consensus seemed to be that "auto pure" is more confusing than its worth.
46 lines
803 B
Text
46 lines
803 B
Text
--
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structure Payload :=
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(key : Nat)
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(val : Nat)
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@[noinline] def get? (p : Payload) (k : Nat) : OptionM Nat :=
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if p.key == k then pure p.val else failure
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inductive T
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| a (i : Nat)
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| b (i : Nat)
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| c (i : Nat)
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| d (i : Nat)
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@[noinline] def foo (p : Payload) : OptionM T :=
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(do
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let i ← get? p 1;
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pure (T.a i))
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<|> (do
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let i ← get? p 2;
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pure (T.b i))
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<|> (do
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let i ← get? p 3;
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pure (T.c i))
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<|> (do
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let i ← get? p 4;
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let i ← get? p 5;
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pure (T.d i))
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def wrongOutput : String :=
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match foo (Payload.mk 1 20) with
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| some (t : T) =>
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match t with
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| T.a i => "1: " ++ toString i
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| T.b i => "2: " ++ toString i
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| T.c i => "3: " ++ toString i
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| T.d i => "4: " ++ toString i
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| none => "5"
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#eval wrongOutput
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def main (xs : List String) : IO Unit :=
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IO.println wrongOutput
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