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23 lines
1.5 KiB
Markdown
23 lines
1.5 KiB
Markdown
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# Notes ~2021.9.24
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## Exploration of `+mink`
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The [`+mink`](https://github.com/urbit/urbit/blob/fa894b9690deae9e2334ccec5492ba90cb0b38f9/pkg/arvo/sys/hoon.hoon#L5978-L6106)
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arm in [`hoon.hoon`](https://github.com/urbit/urbit/blob/master/pkg/arvo/sys/hoon.hoon) is a metacircular Nock interpreter
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intended to be jetted by invoking the host Nock interpreter. In addition to the subject and formula to evaluate, `+mink`
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takes a scry gate which is used to evaluate nock 12 (scry) formulas.
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The jet uses `u3r_mean` to take apart the sample of the `+mink` gate and feeds the resulting nouns to
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`u3n_nock_et`, which runs the interpreter and produces a 'toon',
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Scry gates are kept in a stack because a scry gate may itself scry, and should not re-enter itself.
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## Exceptions in new mars
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### Suboptimal but simple way
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The simple thing to do would be to make every continuation expect a toon and on an error or block result, immediately call
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the next continuation up the stack with it, until a continuation installed e.g. by the +mink jet branched on the result.
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This is effectively writing the interpreter as a CPS/trampoline translation of +mink.
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### Likely more optimal way
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It should be possible to store exception contexts in the hash table: comprising stack pointers for unwinding,
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code pointer to jump to (possibly we could use setjmp/longjmp instead), and a hash reference to the next outermost
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handler. The hash reference to the current exception context would be held in a register. This structure could also hold
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the current scry gate.
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