scryer

This is a Typescript package that embeds Scryer Prolog.

Experimental, API will change. Currently it's (roughly) based on trealla-js's API.

npm install scryer

import { init, Prolog } from "scryer";

await init();

const kb1 = `
:- use_module(library(format)).
:- use_module(library(clpz)).
:- use_module(library(lists)).

sudoku(Rows) :-
length(Rows, 9), maplist(same_length(Rows), Rows),
append(Rows, Vs), Vs ins 1..9,
maplist(all_distinct, Rows),
transpose(Rows, Columns),
maplist(all_distinct, Columns),
Rows = [As,Bs,Cs,Ds,Es,Fs,Gs,Hs,Is],
blocks(As, Bs, Cs),
blocks(Ds, Es, Fs),
blocks(Gs, Hs, Is).

blocks([], [], []).
blocks([N1,N2,N3|Ns1], [N4,N5,N6|Ns2], [N7,N8,N9|Ns3]) :-
all_distinct([N1,N2,N3,N4,N5,N6,N7,N8,N9]),
blocks(Ns1, Ns2, Ns3).
`;

const kb2 = `
problem(1, [[_,_,_,_,_,_,_,_,_],
			[_,_,_,_,_,3,_,8,5],
			[_,_,1,_,2,_,_,_,_],
			[_,_,_,5,_,7,_,_,_],
			[_,_,4,_,_,_,1,_,_],
			[_,9,_,_,_,_,_,_,_],
			[5,_,_,_,_,_,_,7,3],
			[_,_,2,_,1,_,_,_,_],
			[_,_,_,_,4,_,_,_,9]]).
`;

const pl = new Prolog();
pl.consultText(kb1);
pl.consultText(kb2);

const query = pl.query(
	"problem(1, Rows), sudoku(Rows), maplist(portray_clause, Rows).",
);
for (const answer of query) {
	console.log(answer.bindings);
}

For browsers, you can use esm.sh or other CDNs to import it directly:

<script type="module">
	import { init, Prolog } from "https://esm.sh/scryer"; // ideally add version info to the URL, e.g. [email protected]
	await init();
	// query stuff
</script>

Usage

Binding variables

const answer = pl.queryOnce("X is Y * 2.", { bind: { Y: 21 } });
console.log(answer.bindings); // { X: 42, Y: 21 }

Template strings

The prolog string template literal is an easy way to escape terms. Each ${value} will be interpreted as a Prolog term.

import { prolog, Variable } from "scryer";
const answer = pl.queryOnce(
	prolog`atom_chars(${new Variable("X")}, ${"Hello!"}).`,
);
console.log(answer.bindings); // { X: Atom('Hello!') }

Events

Prolog instances are subclasses of EventTarget and emit the following events:

• "ready" -- fired when a query finishes and the interpreter is ready to execute a new query

Development

After cloning the repository, make sure to initialize the submodules:

git submodule update --init --recursive

Alternatively, you can do this directly during the clone:

git clone --recurse-submodules -j8 <repository-url>

make sure to have wasm-pack installed.

Once the submodules are in place and wasm-pack is installed, run the following commands:

npm install
npm run compile    # Installs the WASM package of Scryer Prolog and other dependencies
npm run build      # Transpiles TypeScript code