Good morning Jeremy, et al.,
> Bitcoin Developers,
>
> I'm very excited to introduce Sapio[0] formally to you all.
This seems quite interesting to me as well!
I broadly agree with the rant on monetary units.
In C-Lightning we always (except for some legacy fields that will eventually be
removed) output values as strings with an explicit `msat` unit, even for
onchain values (the smallest of which are satoshi, but for consistency we
always print as millisatoshi), and accept explicit `btc`, `sat`, and `msat`
units.
--
Personally I would have used a non-embedded DSL.
In practice an embedded DSL requires a user to learn two languages --- the
hosting language and the embedded language.
Whereas if you designed a non-embedded DSL, a new user would have to learn only
one language.
For instance, if an error is emitted, then the user has to know whether the
error comes from the hosting language compiler, or the embedded language
implementation.
In a past career embedded DSLs for hardware description languages were being
pushed, and we found that one of the drawbacks was the need to learn as well
the hosting language --- at some point Haskell-embedded DSLs became so
unpopular that anything that was even Haskell-related had a negative reaction
in some hardware design shops.
For example BlueSpec originally was a Haskell-embedded DSL, and eventually
implemented a Verilog-like syntax that was not embedded in Haskell, becoming
BlueSpecSystemVerilog.
Further, as per coding theory, the hosting language is often quite generic and
can talk about anything, including other embedded languages, thus we expect
(all other things being equal) that in general, an utterance in an embedded DSL
will be longer than an utterance in a non-embedded DSL (as there is more things
to talk about, more symbols are necessary, and thus we expect things to be
longer in the generic hosting language).
Whereas a non-embedded DSL can cut away most of the extra verbage needed to
introduce to the hosting language implementation, in order to indicate the
"entry" into the domain-specific language.
--
If my understanding is correct, I seem, that the hosting language is a full,
general, Turing-complete language, that "builds up" a total
(non-Turing-complete) contract description.
I have had (private) speculations before that it would be possible to design a
language with two layers:
* A non-Turing-complete total "base language".
* A syntax meta-language similar to Scheme `syntax-rules`, which constructs
ASTs for the "base language".
Note that Scheme `syntax-rules` is indeed Turing-complete, as a macro can
expand to a form with two lists that form two "ends" of a tape, and act as a
Turing machine on that tape, thus Turing-equivalent.
It is not a general language as it lacks many basic practicalities, but as pure
computation, indeed it is possible to compute anything in that language.
The advantage of this scheme is that the meta-language is executed at language
compile time, and the developer can see (by observing the compilation process)
whether the meta-program halts or not.
However, the end-user executing the program is assured that the program,
delivered as a compiled binary, will indeed terminate, as the base language is
total and non-Turing-complete (i.e. the halting problem is trivial for the base
language --- all programs halt).
I even have started designing a syntax scheme that adds in infix notation and
indent-sensitivity to a Lisp-like syntax, at the cost of disallowing typical
Lisp-like names like `pair?`, e.g.
foo x = value (bar x)
where
bar x = x
is equivalent to:
(`=` (foo x)
(value (bar x)
(where
(`=` (bar x) x))))
I can provide more details if interested.
Note that the base language is not embedded in the meta-language, as the
meta-language is effectively only capable of talking about how the utterance in
the base language is constructed --- the meta-language is not quite general
enough (i.e. the meta-language cannot implement "Hello World").
Thus coding theory should imply that this should lead to more succinct
utterances (in general).
>From this point of view, language design is about striking a balance between
>the low input bandwidth of neurotypical human brains (thus compression is
>needed, i.e. the language encourages succinct programs) and the limited
>processing power of neurotypical human brains (thus decompression speed is
>needed, i.e. it should be obvious what something expands to).
Regards,
ZmnSCPxj
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