Wow this might be the coolest use of Hoot I've seen! I need to run this for myself soon.
deosjr 5 hours ago [-]
Thanks Dave, high praise! I was inspired after seeing you all take over the declarative & minimalist programming room at FOSDEM this year.
If you thought this was cool, wait until you see what I ended up using it for: https://deosjr.github.io/dynamicland/
I personally think this is much cooler :) But it needs some more explaining before I can broadly share, I think.
Now that I have you here, a question: am I correct in thinking that in Hoot, eval in the browser does not currently work with macros?
davexunit 4 hours ago [-]
I'm glad you felt inspired! This Dynamicland implementation looks awesome. I look forward to this being shared to a wider audience. :)
Regarding your question, as of Hoot 0.6.1 we now have a psyntax-based macro expander integrated with eval so you can use syntax-rules and syntax-case. There are still rough edges, though. I'm currently focused on some non-Hoot tasks but the next Hoot priority is to implement a Guile-like REPL and really kick the tires on the interpreter before the 0.7.0 release.
upghost 20 hours ago [-]
Datalog is a syntactic subset of Prolog[1], which this is... not.
I think the most misunderstood thing about Prolog (and Datalog, the functor-free subset of pure Prolog) is that the syntax is really, really important.
It's like, the whole gimmick of the language. It is designed to efficiently and elegantly query and transform itself. If you lose the syntax you lose all of intermediate and advanced Prolog (and Datalog).
Semantics are more important than syntax. Prolog's flexible syntax is a nice-to-have rather than essential when you're in Lisp. And Datalog is purely first-order, so the advanced Prolog you're talking about doesn't exist in it.
However, syntax does matter, and this is not acceptable
I think you could, however, write a bit more Scheme and be able to ask
(?id reachable ?id)
which would be acceptable.
However, the ordering betrays a deeper semantic difference with orthodox Datalog, which is about distinct N-ary relations, like a relational database, not binary relations. This implementation seems to be specific to binary relations, so it's not really Datalog for reasons that go beyond mere syntax.
On the other hand, this (from the initial goal) would be perfectly fine:
Thank you for the feedback! I agree with all of the above.
Should've probably been a bit more clear on the dl-find syntax; I find it just as unacceptable as you do. It is the result of laziness: my intended use of this minimal Datalog does not include any querying whatsoever but abuses fixpoint analysis for side-effects (see https://github.com/deosjr/deosjr.github.io/blob/master/dynam... which I intend to go over in a future post).
I initially had it working like you described but butchered it for the above and haven't repaired it yet (see https://github.com/deosjr/whistle?tab=readme-ov-file#datalog). This version relied on some monstrous eval-hacking using a homebrew Lisp, which I've mostly cleaned up now in this version (https://github.com/deosjr/whistle/blob/main/datalog/datalog.... is a crime, for example).
The semantics are indeed limited to binary relations atm, which I agree is the main thing that disqualifies this as a proper Datalog. iirc the tutorial on Datalog that I based this implementation on only handled triples as well so I stopped there, but extending to N-ary relations is on my list to look into for sure.
kragen 9 hours ago [-]
This sounds very interesting! I'll have to take a look.
I am always worried about posting comments like mine because often people get defensive when I try to engage, as I see it, on substance. Responses like yours make it all worthwhile!
deosjr 8 hours ago [-]
I appreciate it; this kind of exchange is exactly why I read HackerNews.
If you have any good sources on extending Datalog to N-ary relations, I'd love to know. Just had a look at the implementation I based mine on and it exclusively talks about triples: https://www.instantdb.com/essays/datalogjs
Coming from Prolog I'd like to get closer to the original if possible :)
thesz 7 hours ago [-]
They use triples as triplets can represent any n-tuple facts.
E.g., if you have a fact id=(a,b,c,d), you can record triples (id, 1, a), (id, 2, b), (id, 3, c) and (id, 4, d) and reconstruct original fact.
Look at it as columnar storage in databases.
Then, if your query only needs a third value from a 4-tuple facts, you can get only those, ignoring first, second and fourth values. This is what columnar storage engines do.
In fact, I read that one of most efficient datalog engines use relational query execution under the hood.
The paper you'll most probably find interesting is "Better Together: Unifying Datalog and Equality Saturation," but there are many others interesting things there.
deosjr 5 hours ago [-]
Cheers, this is super useful. I will have to do some reading. Being able to build up n-ary predicates using triples that way makes a lot of sense.
jitl 19 hours ago [-]
Shouldn’t lisp macros make it easy to present such a nice syntax? Perhaps the author could easily implement that bit, if not the wide rows. Or is that the point you’re making?
I don't think you need Lisp macros for it; you could use just a regular Lisp function. I don't think the standard R5RS macros are powerful enough to grovel over the query expression to make a list of the free variables, but then, standard Scheme also doesn't have records. I think Guile has a procedural macro system that you could use, but I don't think it would be a good idea.
Yes, I think the semantic divergence is more fundamental. Triple stores and graph databases and binary relations are awesome, but they aren't what Datalog is.
j-pb 18 hours ago [-]
Most database literature simply uses Datalog to mean the query language fragment of conjunctive queries + recursion/fixpoint-iteration and potentially stratified negation.
Yes it started out as a Prolog subset, but the definition as the fragments it supports has become much more prevalent, mainly to contrast it to non-recursive fragments with arbitrary negation (e.g. SQL).
This usage dates back to database literature of the 80s by Ullman et. al.
Runs in the browser using Hoot (https://spritely.institute/hoot/) which compiles Guile Scheme to WebAssembly.
If you thought this was cool, wait until you see what I ended up using it for: https://deosjr.github.io/dynamicland/ I personally think this is much cooler :) But it needs some more explaining before I can broadly share, I think.
Now that I have you here, a question: am I correct in thinking that in Hoot, eval in the browser does not currently work with macros?
Regarding your question, as of Hoot 0.6.1 we now have a psyntax-based macro expander integrated with eval so you can use syntax-rules and syntax-case. There are still rough edges, though. I'm currently focused on some non-Hoot tasks but the next Hoot priority is to implement a Guile-like REPL and really kick the tires on the interpreter before the 0.7.0 release.
I think the most misunderstood thing about Prolog (and Datalog, the functor-free subset of pure Prolog) is that the syntax is really, really important.
It's like, the whole gimmick of the language. It is designed to efficiently and elegantly query and transform itself. If you lose the syntax you lose all of intermediate and advanced Prolog (and Datalog).
[1]: https://en.m.wikipedia.org/wiki/Datalog
However, syntax does matter, and this is not acceptable
as a way to ask I think you could, however, write a bit more Scheme and be able to ask which would be acceptable.However, the ordering betrays a deeper semantic difference with orthodox Datalog, which is about distinct N-ary relations, like a relational database, not binary relations. This implementation seems to be specific to binary relations, so it's not really Datalog for reasons that go beyond mere syntax.
On the other hand, this (from the initial goal) would be perfectly fine:
The orthodox Datalog syntax is:Should've probably been a bit more clear on the dl-find syntax; I find it just as unacceptable as you do. It is the result of laziness: my intended use of this minimal Datalog does not include any querying whatsoever but abuses fixpoint analysis for side-effects (see https://github.com/deosjr/deosjr.github.io/blob/master/dynam... which I intend to go over in a future post). I initially had it working like you described but butchered it for the above and haven't repaired it yet (see https://github.com/deosjr/whistle?tab=readme-ov-file#datalog). This version relied on some monstrous eval-hacking using a homebrew Lisp, which I've mostly cleaned up now in this version (https://github.com/deosjr/whistle/blob/main/datalog/datalog.... is a crime, for example).
The semantics are indeed limited to binary relations atm, which I agree is the main thing that disqualifies this as a proper Datalog. iirc the tutorial on Datalog that I based this implementation on only handled triples as well so I stopped there, but extending to N-ary relations is on my list to look into for sure.
I am always worried about posting comments like mine because often people get defensive when I try to engage, as I see it, on substance. Responses like yours make it all worthwhile!
Coming from Prolog I'd like to get closer to the original if possible :)
E.g., if you have a fact id=(a,b,c,d), you can record triples (id, 1, a), (id, 2, b), (id, 3, c) and (id, 4, d) and reconstruct original fact.
Look at it as columnar storage in databases.
Then, if your query only needs a third value from a 4-tuple facts, you can get only those, ignoring first, second and fourth values. This is what columnar storage engines do.
In fact, I read that one of most efficient datalog engines use relational query execution under the hood.
Take a look here: https://github.com/philzook58/awesome-egraphs
The paper you'll most probably find interesting is "Better Together: Unifying Datalog and Equality Saturation," but there are many others interesting things there.
There is a dl-rule here: https://github.com/deosjr/deosjr.github.io/blob/15b5f7e02153...
Yes, I think the semantic divergence is more fundamental. Triple stores and graph databases and binary relations are awesome, but they aren't what Datalog is.
Yes it started out as a Prolog subset, but the definition as the fragments it supports has become much more prevalent, mainly to contrast it to non-recursive fragments with arbitrary negation (e.g. SQL).
This usage dates back to database literature of the 80s by Ullman et. al.