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 ```
72 lines
1.8 KiB
Text
72 lines
1.8 KiB
Text
def checkM (b : IO Bool) : IO Unit :=
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unless (← b) do throw $ IO.userError "failed"
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abbrev M := ExceptT String $ StateRefT Nat IO
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def f1 : M Nat :=
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throw "error 1"
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def f2 : M Nat :=
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throwThe IO.Error $ IO.userError "error 2"
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def tst1 : M Nat := do
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try
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try f1 finally set 100; IO.println "finisher executed"
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catch _ =>
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get
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def checkE {α ε : Type} [BEq α] (x : IO (Except ε α)) (expected : α) : IO Unit := do
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let r ← x;
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match r with
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| Except.ok a => unless a == expected do throw $ IO.userError "unexpected result"
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| Except.error _ => throw $ IO.userError "unexpected error"
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#eval (tst1.run).run' 0
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#eval checkE ((tst1.run).run' 0) 100
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def tst2 : M Nat :=
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tryCatchThe IO.Error
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(tryFinally f2 (do set 100; IO.println "finisher executed"))
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(fun _ => get)
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#eval (tst2.run).run' 0
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#eval checkE ((tst2.run).run' 0) 100
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def tst3 : M Nat :=
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tryCatchThe IO.Error
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(tryFinally
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(tryFinally f1 (do set 100; IO.println "inner finisher executed"; discard $ f2; pure ()))
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(do modify Nat.succ; IO.println "outer finisher executed"))
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(fun _ => get)
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#eval (tst3.run).run' 0
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#eval checkE ((tst3.run).run' 0) 101
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def tst4 : M Nat := do
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let a ← tryFinally
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(tryFinally (pure 42) (do set 100; IO.println "inner finisher executed"; pure ()))
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(do modify Nat.succ; IO.println "outer finisher executed");
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let s ← get;
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pure (a + s)
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#eval (tst4.run).run' 0
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#eval checkE ((tst4.run).run' 0) 143
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def tst5 : M Nat := do
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let (a, _) ← tryFinally' (pure 42) (fun a? => do IO.println ("finalizer received: " ++ toString a?));
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pure a
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#eval (tst5.run).run' 0
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def tst6 : M Nat := do
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let (a, _) ← tryFinally' f2 (fun a? => do IO.println ("finalizer received: " ++ toString a?));
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pure a
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def tst7 : IO Unit :=
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tryCatchThe IO.Error (do discard $ (tst6.run).run' 0; pure ()) (fun _ => IO.println "failed as expected")
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#eval tst7
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