lean4-htt/tests/lean/pureCoeIssue.lean.expected.out at 298bdfdcdebc2d0f18fbcce181cab4e05fcecce9 - max/lean4-htt - maxgit: wireguard access, git repository.

max/lean4-htt

Leonardo de Moura 06ad52575a feat: force users to use discard when action result is not being bound and it is not PUnit

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
```

2020-12-08 06:14:48 -08:00

16 lines

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Raw Blame History

 pureCoeIssue.lean:6:2: error: application type mismatch
   bind f1
 argument
   f1
 has type
   Nat → IO Unit
 but is expected to have type
   IO PUnit
 pureCoeIssue.lean:14:2: error: application type mismatch
   bind (f2 10)
 argument
   f2 10
 has type
   Nat → IO Unit
 but is expected to have type
   IO PUnit