triska
commented
1 month ago Thank you a lot for working on this! I can contribute a few points regarding terminology:
An answer is something we get in response to a query. In Scryer Prolog, an answer always has the form of a goal that is declaratively equivalent to the query.
The ISO standard defines a goal as:
3.81 goal: A predication which is to be executed (see body, query, and 7.7.3).
And also:
5.3 Prolog goal A conforming Prolog goal is one whose execution is defined by the constructs specified in this part of ISO/IEC 13211, and the implementation defined and implementation specific features supported by the processor. A strictly conforming Prolog goal is one whose execution is defined by the constructs specified in this part of ISO/IEC 13211, and the implementation defined features supported by the processor.
This is very broad. For example, (f ; g ; h) is a goal. At the same time, each of f, g and h is also a goal!
Therefore, when we see for example:
?- length(Ls, L). Ls = [], L = 0 ; Ls = [_A], L = 1 ; Ls = [_A,_B], L = 2 ; Ls = [_A,_B,_C], L = 3 ; ... .
then, in addition to the entire answer, each of the disjuncts is also called an answer! We currently lack the terminology to properly distinguish these cases!
A solution is an answer that grounds all variables that appear in the query. In the above example, Ls = [], L = 0 is a solution, whereas Ls = [_A], L = 1 is an answer but not a solution. A single answer may describe infinitely many concrete solutions.
In the above example, all answers are answer substitutions, i.e., answers of the form Var1 = T1, Var2 = T2, .... A single conjunct of an answer substitution is also called a binding, such as L = 3.
An answer can also be an exception, reported (as all cases above) as a goal; a goal that yields that exception.
An answer may also include residual goals. Since all answers (including answer substitutions) are goals, one could all classify them as "residual goals", but we normally use "residual goals" only to mean pending constraints that are not trivial in the sense that: they are not answer substitutions. An example of a residual goal is dif(X, f(b)). Residual goals may occur by themselves, or together with answer substitutions. An answer that contains residual goals is also called a conditional solution, because it only implies solutions if the residual constraints can be satisfied.
The answers true and false are not called "residual goals" even though they are also goals.
bakaq
jjtolton
I think that if we are going to do things like #2475 (we did, it's merged), that is a breaking change in the Rust library interface, then we should use this opportunity to actually improve a lot of things and make the API more friendly, consistent and resilient to future changes. I going to use this as a tracking issue for that endeavor (I will keep this updated and link relevant issues and PRs). Basically everything here will be a breaking change for the
scryer_prologRust library (that means landing on version0.10.0or later). Feedback (like on if this is even a good idea) and suggestions are very welcome!scryer_prolog::{atom, machine::{Machine, INTERRUPT, config::{MachineConfig, StreamConfig}}}to be public (and we could probably put all of that in aMachine::run_binary()method and have just that be public), and the library use case only really needsscryer_prolog::machine::{parsed_results::*, lib_machine::*}additionally. We probably don't need all the current public methods onMachineto be public also. Everything else should be at leastpub(crate), if not stricter.MachineConfigandStreamConfig(or analogous types) will probably have to be public, but to enable changing their internals in the future (which to me seems very likely) without breaking API,MachineConfigshould have private fields and StreamConfig should be#[non_exhaustive]. ShouldValue(or analogous) also be non-exhaustive/opaque (for future Unum support for example)?Valuetype inparsed_results.rs, but I think a better name would beTermorPrologTerm.QueryStateis an iterator of (Results of)QueryResolutionLine, and I don't know exactly what a good name would be here (PrologAnswer? What is the diferent between answer, solution, variable substitution, etc? Is there even a consensus on meaning here?).2497
Debug,Eq,serde::Serialize(probably behind a feature), etc, on everything that makes sense.Into<String>instead ofString, orIntoIterator<T>instead ofVec<T>, when it makes sense.ValueandQueryResolutionthat ideally can be extended in the future to support things like residual goals. I made an initial proposal here.2493
#![deny(missing_docs)].