2652cc18b8
This PR standardizes error messages by quoting names with backticks. The changes were automated, so some cases may still be missing.
61 lines
1.8 KiB
Text
61 lines
1.8 KiB
Text
/-!
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# `partial` inhabitation with delta derivation
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-/
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set_option pp.mvars false
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/-!
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In the following, `partial` needs to unfold the return type to find an Inhabited instance.
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-/
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def MyGreatType (α : Type) := α × α
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partial def myLessGreatFunction (n : Nat) : MyGreatType Nat := myLessGreatFunction n
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/-!
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In the following, it needs to unfold underneath a forall.
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-/
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def MyGreaterType (α : Type) := α → MyGreatType α
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partial def myEvenLessGreatFunction (n : Nat) : MyGreaterType Nat := myEvenLessGreatFunction n
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/-!
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Regression test: can use existing parameter.
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-/
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partial def test1 (x : α) : α := test1 x
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/-!
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Regression test: can use Inhabited instance in parameter list.
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-/
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partial def test2 [Inhabited α] (n : Nat) : α := test2 n
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/-!
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Regression test: can use Nonempty instance in parameter list.
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-/
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partial def test3 [Nonempty α] (n : Nat) : α := test3 n
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/-!
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Error message.
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-/
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/--
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error: failed to compile 'partial' definition `test4`, could not prove that the type
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{α : Sort u_1} → Nat → α
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is nonempty.
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This process uses multiple strategies:
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- It looks for a parameter that matches the return type.
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- It tries synthesizing 'Inhabited' and 'Nonempty' instances for the return type, while making every parameter into a local 'Inhabited' instance.
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- It tries unfolding the return type.
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If the return type is defined using the 'structure' or 'inductive' command, you can try adding a 'deriving Nonempty' clause to it.
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-/
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#guard_msgs in partial def test4 (n : Nat) : α := test4 n
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/-!
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Add arguments as inhabited instances.
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Example adapted from https://leanprover.zulipchat.com/#narrow/channel/113489-new-members/topic/Why.20return.20type.20of.20partial.20function.20MUST.20.60inhabited.60.3F/near/477905312
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-/
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inductive ListNode where
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| mk : Nat → Option ListNode → ListNode
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partial def checkMyList (head : ListNode) : Bool × ListNode := checkMyList head
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