[herd] More implicit transitive relations in the Cat interpreter#1719
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[herd] More implicit transitive relations in the Cat interpreter#1719
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maranget
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| begin | ||
| try | ||
| let es,saw_seq = as_plus_args false x es in | ||
| if saw_seq then Some (x,es) else None |
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Could we have a warning that the rec flag is useless in that case?
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I'd rather leave this to another PR.
…reter We notice that `(...|r+|...)+` is `(...|r|...)+` and thus also that irrefexivity of `(...|r+|...)+` is equivalent to acyclicity of `(...|r|...)`. The process may be interesting because we also identify some of the recursive definitions that are equivalent to a transitive closure and represent them as (implicit) transitive closure, thereby saving some transitive closure operations. In practice, improvements are barely noticeable.
maranget
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We take advantage of union commutativity for performing this petty optimisation.
More precisely, bindings of the form `x = e`, where the expression `e`potentially reduces to some transitive closure (such as `e+`) are handled specially, by accepting an implicit transitive closure as a result.
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We notice that
(...|r+|...)+is(...|r|...)+and thus also that irrefexivity of(...|r+|...)+is equivalent to acyclicity of(...|r|...)The process may be interesting because we also identify some of the recursive definitions that are equivalent to a transitive closure and represent them as (implicit) transitive closure, thereby saving some transitive closure operations.
However, to avoid the repetive evaluation of bound implicit transitive closures to explicit ones, we rely on an additionnal environment for implicitly transitive relations, introducing minor extra costs.
In the end, improvements are barely noticeable, but the interpreter should gain as regards performance robustness.