fb0c46a011
This implements the `termination_by structural` syntax proposed in #3909. I went with `termination_by structural` over, say, `termination_by (config := {method := .structural})` mainly because it was easier to get going (otherwise I’d have to look into how to define recursive parsers, as `Parser.config` depends on `term` and `termination_by` is part of term. But also because I find it more ergonomic and aesthetic as a user. But syntax can still change. The `termination_by?` syntax will no longer force well-founded recursion, and instead the inferred `termination_by structurally` annotation will be shown if structural termination is possible. While I was it, this fixes #4546 the easy way (log errors about but otherwise ignore incomplete `termination_by` sets for mutual recursion). Maybe we get multiple replacements (#4551), but even then this this good behavior. Involves a bit of shuffling around `TerimationHints` (now validated for a clique already by `PreDefinition.main`) and `TerminationArguments` (now lifted out of the `WF` namespace, and a bit simplified). Fixes #3909 --------- Co-authored-by: Richard Kiss <him@richardkiss.com>
34 lines
877 B
Text
34 lines
877 B
Text
def ackermann (n m : Nat) := match n, m with
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| 0, m => m + 1
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| .succ n, 0 => ackermann n 1
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| .succ n, .succ m => ackermann n (ackermann (n + 1) m)
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termination_by?
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--^ codeAction
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-- Check hat we print this even if there is only one plausible measure
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def onlyOneMeasure (n : Nat) := match n with
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| 0 => 0
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| .succ n => onlyOneMeasure n
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termination_by?
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--^ codeAction
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def anonymousMeasure : Nat → Nat
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| 0 => 0
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| .succ n => anonymousMeasure n
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termination_by?
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--^ codeAction
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-- Check hat we print this even if there is only one plausible measure
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def onlyOneMeasureWF (n : Nat) := match n with
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| 0 => 0
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| .succ n => onlyOneMeasureWF n
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termination_by?
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--^ codeAction
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decreasing_by decreasing_tactic
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def anonymousMeasureWF : Nat → Nat
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| 0 => 0
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| .succ n => anonymousMeasureWF n
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termination_by?
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--^ codeAction
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decreasing_by decreasing_tactic
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