3a309ba4eb
This PR improves the error message encountered in the case of a type class instance resolution failure, and adds an error explanation that discusses the common new-user case of binary operation overloading and points to the `trace.Meta.synthInstance` option for advanced debugging. ## Example ```lean4 def f (x : String) := x + x ``` Before: ``` failed to synthesize HAdd String String ?m.5 Hint: Additional diagnostic information may be available using the `set_option diagnostics true` command. ``` After: ``` failed to synthesize instance of type class HAdd String String ?m.5 Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command. Error code: lean.failedToSynthesizeTypeclassInstance [View explanation](https://lean-lang.org/doc/reference/latest/find/?domain=Manual.errorExplanation&name=lean.failedToSynthesizeTypeclassInstance) ``` The error message is changed in three important ways: * Explains *what* failed to synthesize, using the "type class" terminology that's more likely to be recognized than the "instance" terminology * Points to the `trace.Meta.synthInstance` option which is otherwise nearly undiscoverable but is quite powerful (see also leanprover/reference-manual#663 which is adding commentary on this option) * Gives an error explanation link (which won't actually work until the next release after this is merged) which prioritizes the common-case explanation of using the wrong binary operation
60 lines
1.9 KiB
Text
60 lines
1.9 KiB
Text
open List MergeSort Internal
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-- If we omit the comparator, it is filled by the autoparam `fun a b => a ≤ b`
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example : mergeSort [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5] = [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9] :=
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by native_decide
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example : mergeSort [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5] (· ≤ ·) = [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9] :=
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by native_decide
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example : mergeSort [3, 100 + 1, 4, 100 + 1, 5, 100 + 9, 2, 10 + 6, 5, 10 + 3, 5] (fun x y => x/10 ≤ y/10) = [3, 4, 5, 2, 5, 5, 16, 13, 101, 101, 109] :=
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by native_decide
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example : mergeSortTR [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5] = [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9] :=
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by native_decide
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example : mergeSortTR [3, 100 + 1, 4, 100 + 1, 5, 100 + 9, 2, 10 + 6, 5, 10 + 3, 5] (fun x y => x/10 ≤ y/10) = [3, 4, 5, 2, 5, 5, 16, 13, 101, 101, 109] :=
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by native_decide
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example : mergeSortTR₂ [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5] = [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9] :=
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by native_decide
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example : mergeSortTR₂ [3, 100 + 1, 4, 100 + 1, 5, 100 + 9, 2, 10 + 6, 5, 10 + 3, 5] (fun x y => x/10 ≤ y/10) = [3, 4, 5, 2, 5, 5, 16, 13, 101, 101, 109] :=
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by native_decide
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/-!
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# Behaviour of mergeSort when the comparator is not provided, but typeclasses are missing.
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-/
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inductive NoLE
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| mk : NoLE
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/--
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error: could not synthesize default value for parameter 'le' using tactics
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---
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error: failed to synthesize instance of type class
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LE NoLE
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Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command.
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-/
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#guard_msgs in
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example : mergeSort [NoLE.mk] = [NoLE.mk] := sorry
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inductive UndecidableLE
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| mk : UndecidableLE
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instance : LE UndecidableLE where
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le := fun _ _ => true
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/--
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error: could not synthesize default value for parameter 'le' using tactics
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---
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error: Type mismatch
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a ≤ b
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has type
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Prop
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but is expected to have type
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Bool
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-/
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#guard_msgs in
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example : mergeSort [UndecidableLE.mk] = [UndecidableLE.mk] := sorry
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