06ad52575a
After this commit, we have to use an explicit `discard` in code such as ``` def g (x : Nat) : IO Nat := ... def f (x : Nat) : IO Unit := do discard <| g x -- type error without the `discard` IO.println x ``` Motivation: prevent users from making mistakes such as ``` def f (xs : Array Nat) : IO Unit := do xs.set! 0 1 IO.println xs ``` when they meant to write ``` def f (xs : Array Nat) : IO Unit := do let xs := xs.set! 0 1 IO.println xs ```
24 lines
599 B
Text
24 lines
599 B
Text
--
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def inc (r : IO.Ref Nat) : IO Unit := do
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let v ← r.get;
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r.set (v+1);
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IO.println (">> " ++ toString v)
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def initArray (r : IO.Ref (Array Nat)) (n : Nat) : IO Unit :=
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n.forM $ fun i => do
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r.modify $ fun a => a.push (2*i)
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def showArrayRef (r : IO.Ref (Array Nat)) : IO Unit := do
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let a ← r.swap ∅;
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a.size.forM (fun i => IO.println ("[" ++ toString i ++ "]: " ++ toString (a.get! i)));
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discard $ r.swap a;
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pure ()
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def tst (n : Nat) : IO Unit := do
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let r₁ ← IO.mkRef 0;
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n.forM fun _ => inc r₁;
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let r₂ ← IO.mkRef (∅ : Array Nat);
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initArray r₂ n;
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showArrayRef r₂
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#eval tst 10
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