17825bf81d
by showing the matrix of calls and measures, and what we know about that
call (=, <, ≤, ?), e.g.
guessLexFailures.lean:27:0-33:31: error: Could not find a decreasing
measure.
The arguments relate at each recursive call as follows:
(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
x1 x2 x3
1) 29:6-25 = = =
2) 30:6-23 = ? <
3) 31:6-23 < _ _
Please use `termination_by` to specify a decreasing measure
It’s a bit more verbose for mutual functions.
It will use the user-specified argument names for functions written
```
foo (n : Nat) := …
```
but not with pattern matching like
```
foo : Nat → …
| n => …
```
This can be refined later and separately (and maybe right away in
`expandMatchAltsWhereDecls`).
38 lines
1 KiB
Text
38 lines
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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structural recursion does not handle mutually recursive functions
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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 (a✝ : Nat) : Nat
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1
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2
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terminationFailure.lean:24:9-24:12: error: fail to show termination for
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h
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with errors
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argument #1 was not used for structural recursion
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failed to eliminate recursive application
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h x
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structural recursion cannot be used
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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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