Ask Ryan to expose the backtrack continuation. Then accumulate
the anti-effects and attach them to the backtrack continuation.
If it is thrown, it’ll automatically undo the effects.
I bet this will be useful in a more general setting.
[See Prolog implementation as embeddings.]
> On Jul
It is not uncommon for me, as a macro writer, to need to perform
syntax-local-value on some identifier, then record the disappeared use
in the resulting expansion. The syntax-local-value/record helper makes
this much easier, but it still requires some manual failure logic. I was
thinking it would
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