3ab2c714ec
the support for mutual structural recursion (new since #4575) is extended so that Lean tries to infer it even without annotations. * The error message when termination checking fails looks quite different now. Maybe a bit better, maybe with more room for improvements. * If there are too many combinations (with an arbitrary cut-off) for a given argument type, it will just give up and ask the user to use `termination_by structural`. * It is now legal to specify `termination_by structural` on not necessarily all functions of a clique; this simply restricts the combinations of arguments that Lean considers. --------- Co-authored-by: Tobias Grosser <tobias@grosser.es>
42 lines
1.1 KiB
Text
42 lines
1.1 KiB
Text
terminationFailure.lean:7:2-7:3: error: fail to show termination for
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f.g
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f
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with errors
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failed to infer structural recursion:
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Cannot use parameters #1 of f.g and x of f:
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failed to eliminate recursive application
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_root_.f x
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Could not find a decreasing measure.
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The arguments relate at each recursive call as follows:
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(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
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Call from f.g to f at 9:9-12:
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x1
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x =
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Call from f to f.g at 3:4-7:
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x
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x1 =
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Please use `termination_by` to specify a decreasing measure.
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f (x : Nat) : Nat
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f.g : Nat → Nat
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1
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2
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terminationFailure.lean:20:4-20:5: error: fail to show termination for
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h
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with errors
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failed to infer structural recursion:
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Cannot use parameter x:
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failed to eliminate recursive application
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h x
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failed to prove termination, possible solutions:
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- Use `have`-expressions to prove the remaining goals
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- Use `termination_by` to specify a different well-founded relation
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- Use `decreasing_by` to specify your own tactic for discharging this kind of goal
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x : Nat
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⊢ False
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h (x : Nat) : Foo
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Foo.a
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