jsprolog

# jsprolog

What is it?

It's a simple Prolog interpreter written with TypeScript. I've adapted it from Jan's javascript Prolog interpreter because I needed a convenient automated theorem proving engine in JavaScript.

What it can do

It can solve simple stuff, for instance N-queen problem. It supports tail recursion.

Limitations

• Parser doesn't support operators. Use function call notation: =(X, Y), is(Z, +(1, X)).
• It has a very limited set of built-in predicates.
• Current implementation is slow. Finding all solutions of N-queen problem takes about 25 seconds on Intel i5-3570.

Preliminary string support

Jsprolog features rudimental support for strings:

• Double quoted text is parsed as a list of character codes.
• Use \" to mask double quote (NB: remember to escape \ as well in javascript strings: "looks \\\"pretty\\\"" )
• No built-in predicates to work with strings.
• Will be replaced with string type in future.

How to use

npm i jsprolog

Please note that the project is far from stabilization and the API will surely change at some point in the future.

var Prolog = require('jsprolog');
var db = Prolog.Parser.parse("member(X,[X|R]). member(X, [Y | R]) :- member(X, R)."),
    query = Prolog.Parser.parseQuery("member(X,[a,b,c]),member(Y,[1,2,3])."),    
    iter = Prolog.Solver.query(db, query);
while(iter.next()){
    console.log("X = ", iter.current.X, ", Y = ", iter.current.Y);
}

Also refer to specs/prologSolverSpec.js for usage examples.

Supported built-in predicates

Predicate	Notes
=/2	Doesn't support cyclic terms.
!/0
fail/0
call/1
findall/3
is/2	Supports only +,-,/,*. Silently fails on error.