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 ```
23 lines
475 B
Text
23 lines
475 B
Text
def f (x : Nat) : IO Unit := do
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x -- Error
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IO.println x
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def f' (x : Nat) : IO Unit := do
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discard x
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IO.println x
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def g (xs : Array Nat) : IO Unit := do
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xs.set! 0 1 -- Error
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IO.println xs
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def g' (xs : Array Nat) : IO Unit := do
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discard <| xs.set! 0 1 -- Error
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IO.println xs
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def h (xs : Array Nat) : IO Unit := do
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pure (xs.set! 0 1) -- Error
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IO.println xs
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def h' (xs : Array Nat) : IO Unit := do
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discard <| pure (xs.set! 0 1) -- Error
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IO.println xs
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