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Trealla is one of the most interesting new Prolog systems: Notably, as in other new systems such as Scryer and Tau Prolog and ichiban/prolog, the default settin

by triska 4y ago

Trealla is one of the most interesting new Prolog systems: Notably, as in other new systems such as Scryer and Tau Prolog and ichiban/prolog, the default setting of the Prolog flag double_quotes is chars, and therefore lists of characters can be conveniently written as double-quoted strings in Prolog code. Second, as in Scryer Prolog, such lists are very compactly encoded internally, making Trealla suitable for analyzing and processing very large amounts of text conveniently and efficiently. In addition, file contents can be processed directly with Prolog's built-in grammar formalism, Definite Clause Grammars (DCGs): Internally, Trealla maps the file contents directly to memory with mmap(2), an innovation that is currently unique to Trealla! There is also a recent WASM embedding: https://github.com/guregu/trealla-go https://github.com/guregu/trealla-go Thank you a lot Andrew and all contributors for your great work on Trealla! It is to be hoped that these implementation techniques are also adopted in other Prolog systems!

mst 4y ago
Ah, so 'codes' is the setting for that flag that erlang's behaviour matches. Which in an old-school prolog makes complete sense, but if you can encode the 'chars' variant efficiently then that works out fine. For those not that prolog literate (like me): https://stackoverflow.com/questions/8264699/what-is-the-difference-between-and-in-prolog/8269897#8269897 https://stackoverflow.com/questions/8264699/what-is-the-diff... seems to help.
- triska 4y ago
  Yes, that's correct! Interestingly, Erlang does encode lists of codes efficiently internally! The advantage of chars is that in this way, we obtain much more readable answers to queries! The very first Prolog system, Prolog 0, already used lists of characters for strings. Later systems tended to interpret them as lists of codes, and we now see several new Prolog systems that (again) interpret them as characters.
billfruit 4y ago
How does this and Scryer, Tau all compare with the SWI?
- triska 4y ago
  Apart from different implementation languages and techniques (Rust/JavaScript/C, WAM/AST interpretation etc.), one of the most striking and impactful differences is that Scryer, Tau and Trealla Prolog aspire towards ISO conformance, i.e., they try to adhere to the Prolog standard, whereas SWI intentionally does not adhere to the standard: https://www.complang.tuwien.ac.at/ulrich/iso-prolog/SWI7_and_ISO https://www.complang.tuwien.ac.at/ulrich/iso-prolog/SWI7_and... Scryer already provides an interface for attributed variables that is compatible to SICStus Prolog, one of the most sophisticated Prolog systems, and uses it to implement various constraints such as dif/2 (also rudimentarily available in Trealla, but not yet in Tau), Boolean constraints etc., which I hope become available in Tau, Trealla and other upcoming systems such as ichiban/prolog in due time.
  - billfruit 4y ago
    Is ISO adherence a big deal? Because SWI seems quite mature and featurefull. The impression I got is that SWI is to Prolog, what GHC is to Haskell.
    - triska 4y ago
      Adherence to standards matters a lot for example in several kinds of governmental organizations, banks, the medical industry etc. If you want to use a Prolog system in safety-critical areas, it is best, and often in fact required by internal and external guidelines, to choose vendors who are committed to upholding standards: This simplifies procurement, settling legal disputes and warranty questions, it reduces the risk of depending on a single vendor etc. Standards are also important when creating teaching material, and obviously for compatibility and interoperability between systems. I therefore recommend to use and provide Prolog systems with strong commitment to the Prolog ISO standard.
      - billfruit 4y ago
        Standards aren't that much of a constraint for SQL/databases, for example. Mostly one works with the dialect that is used by the specific implementation. Moreover standard hasn't kept pace with innovation by various vendors. So in the case of SQL more than de-jure standards, it is the generalized set of features that popular implementations support that matters. Isn't that the case with Prolog? So I'd be more interested in reasons other than literal adherence to de-jure standards.
jfmc 4y ago
I really recognize the value of new implementations and the fact that each of them is filling a hole that old implementations do not cover (like new platform support, more embeddings, etc.). But I have a controversial question: why is it better to start a system from scratch than contributing and helping to other less known, long running systems (Yap, XSB, ECLiPSe, Ciao, gprolog, B-Prolog, etc.)? In the old times, a system became popular because you read a research paper which described carefully the implementation decisions and did good performance evaluations. Papers were reviewed and trusted, you could get objective information about why the implementation was good or not. This helped advance the state of the art. Nowadays, this is completely broken and it is strangely feeling like a "popularity" contest and a social game. For example, some users were surprised about the performance of WASM-compiled Ciao Playground: https://ciao-lang.org/playground/ that despite being x2 slower than native, is faster than other popular Prolog implementations. We needed to tweet about it and use the forum of another popular Prolog system to have any visibility. Despite that, this fact will soon be ignored and buried. When looking at the VM of each of the systems, we know why this happens, but the expertise of the people who wrote earlier Prolog systems, many of them run perfectly fine and blazingly fast in modern machines, is being lost. Of course, we learned a long time ago that the selection of benchmarks is really complex. You can pick whatever is needed to make your system shine. Ciao Prolog is extremely fast for some benchmarks but it can also be much slower in others. My claim is that despite it is cool to have new and nice Prolog implementations, this is adding a lot of noise and we are repeating mistakes from the past and going in the wrong direction: - There is no incentive for proper benchmarking (e.g., should I implement mmap-based file mapping? when does it help? is it a good idea?) - The literature is being ignored (e.g., who reads and compares with Paul Tarau or Bart Demoen implementation papers?) - VM and libraries should be independent (it should be possible to implement a new VM while not requiring to reimplementing the whole set of libraries) - Systems copy/reimplement features without proper recognition of the original system (e.g., once a technique is adopted by the popular system, the original is forgotten, who knows that JITI was originally developed by Vitor Santos Costa in YAP?). - The community is extremely fragmented. I wonder if it would be possible to create a more healthy Prolog forum which prioritizes ideas, authors, and results. Going through twitter, discourse, github discussions, github issues, of each of our individual Prolog system is NOT a solution. Each of us looking at decades of research papers and reproducing them in each of our systems is also not a good idea (indeed the unique advantage of old systems is that it takes decades to incorporate some of these ideas). Moreover, there are still many unsolved problems in modern Prolog systems that can only be addressed as programming language research.

by triska 4y ago

mst 4y ago

Ah, so 'codes' is the setting for that flag that erlang's behaviour matches. Which in an old-school prolog makes complete sense, but if you can encode the 'chars' variant efficiently then that works out fine. For those not that prolog literate (like me): https://stackoverflow.com/questions/8264699/what-is-the-difference-between-and-in-prolog/8269897#8269897 https://stackoverflow.com/questions/8264699/what-is-the-diff... seems to help.

triska 4y ago
Yes, that's correct! Interestingly, Erlang does encode lists of codes efficiently internally! The advantage of chars is that in this way, we obtain much more readable answers to queries! The very first Prolog system, Prolog 0, already used lists of characters for strings. Later systems tended to interpret them as lists of codes, and we now see several new Prolog systems that (again) interpret them as characters.

billfruit 4y ago

How does this and Scryer, Tau all compare with the SWI?

triska 4y ago
Apart from different implementation languages and techniques (Rust/JavaScript/C, WAM/AST interpretation etc.), one of the most striking and impactful differences is that Scryer, Tau and Trealla Prolog aspire towards ISO conformance, i.e., they try to adhere to the Prolog standard, whereas SWI intentionally does not adhere to the standard: https://www.complang.tuwien.ac.at/ulrich/iso-prolog/SWI7_and_ISO https://www.complang.tuwien.ac.at/ulrich/iso-prolog/SWI7_and... Scryer already provides an interface for attributed variables that is compatible to SICStus Prolog, one of the most sophisticated Prolog systems, and uses it to implement various constraints such as dif/2 (also rudimentarily available in Trealla, but not yet in Tau), Boolean constraints etc., which I hope become available in Tau, Trealla and other upcoming systems such as ichiban/prolog in due time.
- billfruit 4y ago
  Is ISO adherence a big deal? Because SWI seems quite mature and featurefull. The impression I got is that SWI is to Prolog, what GHC is to Haskell.
  - triska 4y ago
    Adherence to standards matters a lot for example in several kinds of governmental organizations, banks, the medical industry etc. If you want to use a Prolog system in safety-critical areas, it is best, and often in fact required by internal and external guidelines, to choose vendors who are committed to upholding standards: This simplifies procurement, settling legal disputes and warranty questions, it reduces the risk of depending on a single vendor etc. Standards are also important when creating teaching material, and obviously for compatibility and interoperability between systems. I therefore recommend to use and provide Prolog systems with strong commitment to the Prolog ISO standard.
    - billfruit 4y ago
      Standards aren't that much of a constraint for SQL/databases, for example. Mostly one works with the dialect that is used by the specific implementation. Moreover standard hasn't kept pace with innovation by various vendors. So in the case of SQL more than de-jure standards, it is the generalized set of features that popular implementations support that matters. Isn't that the case with Prolog? So I'd be more interested in reasons other than literal adherence to de-jure standards.

jfmc 4y ago

I really recognize the value of new implementations and the fact that each of them is filling a hole that old implementations do not cover (like new platform support, more embeddings, etc.). But I have a controversial question: why is it better to start a system from scratch than contributing and helping to other less known, long running systems (Yap, XSB, ECLiPSe, Ciao, gprolog, B-Prolog, etc.)? In the old times, a system became popular because you read a research paper which described carefully the implementation decisions and did good performance evaluations. Papers were reviewed and trusted, you could get objective information about why the implementation was good or not. This helped advance the state of the art. Nowadays, this is completely broken and it is strangely feeling like a "popularity" contest and a social game. For example, some users were surprised about the performance of WASM-compiled Ciao Playground: https://ciao-lang.org/playground/ that despite being x2 slower than native, is faster than other popular Prolog implementations. We needed to tweet about it and use the forum of another popular Prolog system to have any visibility. Despite that, this fact will soon be ignored and buried. When looking at the VM of each of the systems, we know why this happens, but the expertise of the people who wrote earlier Prolog systems, many of them run perfectly fine and blazingly fast in modern machines, is being lost. Of course, we learned a long time ago that the selection of benchmarks is really complex. You can pick whatever is needed to make your system shine. Ciao Prolog is extremely fast for some benchmarks but it can also be much slower in others. My claim is that despite it is cool to have new and nice Prolog implementations, this is adding a lot of noise and we are repeating mistakes from the past and going in the wrong direction: - There is no incentive for proper benchmarking (e.g., should I implement mmap-based file mapping? when does it help? is it a good idea?) - The literature is being ignored (e.g., who reads and compares with Paul Tarau or Bart Demoen implementation papers?) - VM and libraries should be independent (it should be possible to implement a new VM while not requiring to reimplementing the whole set of libraries) - Systems copy/reimplement features without proper recognition of the original system (e.g., once a technique is adopted by the popular system, the original is forgotten, who knows that JITI was originally developed by Vitor Santos Costa in YAP?). - The community is extremely fragmented. I wonder if it would be possible to create a more healthy Prolog forum which prioritizes ideas, authors, and results. Going through twitter, discourse, github discussions, github issues, of each of our individual Prolog system is NOT a solution. Each of us looking at decades of research papers and reproducing them in each of our systems is also not a good idea (indeed the unique advantage of old systems is that it takes decades to incorporate some of these ideas). Moreover, there are still many unsolved problems in modern Prolog systems that can only be addressed as programming language research.