2652cc18b8
This PR standardizes error messages by quoting names with backticks. The changes were automated, so some cases may still be missing.
50 lines
1.7 KiB
Text
50 lines
1.7 KiB
Text
/-!
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# Tests of the 'cases' tactic
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-/
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/-!
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Error messages when not an inductive type.
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-/
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/--
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error: Tactic `cases` failed: major premise type is not an inductive type
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Prop
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Explanation: the `cases` tactic is for constructor-based reasoning as well as for applying custom cases principles with a 'using' clause or a registered '@[cases_eliminator]' theorem. The above type neither is an inductive type nor has a registered theorem.
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Consider using the 'by_cases' tactic, which does true/false reasoning for propositions.
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p : Prop
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⊢ True
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-/
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#guard_msgs in
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example (p : Prop) : True := by
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cases p
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/--
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error: Tactic `cases` failed: major premise type is not an inductive type
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Type
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Explanation: the `cases` tactic is for constructor-based reasoning as well as for applying custom cases principles with a 'using' clause or a registered '@[cases_eliminator]' theorem. The above type neither is an inductive type nor has a registered theorem.
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Type universes are not inductive types, and type-constructor-based reasoning is not possible. This is a strong limitation. According to Lean's underlying theory, the only provable distinguishing feature of types is their cardinalities.
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α : Type
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⊢ True
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-/
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#guard_msgs in
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example (α : Type) : True := by
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cases α
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/--
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error: Tactic `cases` failed: major premise type is not an inductive type
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Bool → Bool
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Explanation: the `cases` tactic is for constructor-based reasoning as well as for applying custom cases principles with a 'using' clause or a registered '@[cases_eliminator]' theorem. The above type neither is an inductive type nor has a registered theorem.
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f : Bool → Bool
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⊢ True
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-/
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#guard_msgs in
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example (f : Bool → Bool) : True := by
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cases f
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