pt-lisp/implementations/js/evaluator.js

import { DataTypes, Cons, Nil } from './datatypes.js';
import { Env } from './env.js';

export class Evaluator {
    static async expand(sexp, macros) {
	if (sexp.type === DataTypes.Cons) {
	    const op = await Evaluator.expand(sexp.car, macros)
	    if (op.type === DataTypes.SpecialForm) {
		return await op.value(sexp.cdr, macros, macros);
	    } else if (op.type === DataTypes.Macro) {
		return await op.value(
		    await Cons.map(sexp.cdr,
				   async o => await Evaluator.expand(o, macros)));
		// return (sexp.cdr.type === DataTypes.Nil
		// 	    ? sexp.cdr
		// 	    : Cons.reverse(await Cons.reduce(
		// 		sexp.cdr,
		// 		(p, o) => new Cons(await Evaluator.expand(o, macros), p),
		// 		new Nil())))
		// 	.then(opts => op.value(opts));
	    } else if (sexp.type === DataTypes.Symbol) {
		return Env.find(macros, sexp.value) || sexp;
	    }
	    
	    return sexp;
	}
	
	if (sexp.type === DataTypes.Symbol) {
	    return Env.find(macros, sexp.value) || sexp;
	}
	
	return sexp;
    }

    static async eval(sexp, env, macros) {
	sexp = await Evaluator.expand(sexp, macros)
	if (sexp.type === DataTypes.Cons) {
	    const op = await Evaluator.eval(sexp.car, env, macros)
	    if (op.type === DataTypes.SpecialForm) {
		return await op.value(sexp.cdr, env, macros);
	    } else if (op.type === DataTypes.Function) {
		return await op.value(await Cons.map(sexp.cdr, async o => Evaluator.eval(o, env, macros)));
		// return (sexp.cdr.type === DataTypes.Nil
		// 	? Promise.resolve(sexp.cdr)
		// 	: Cons.reduce(
		// 	    sexp.cdr,
		// 	    (p, o) => p.then(v => Evaluator.eval(o, env, macros)
		// 			     .then(ve => new Cons(ve, v))),
		// 	    Promise.resolve(new Nil()))
		// 	.then(v => Cons.reverse(v)))
		//     .then(opts => op.value(opts));
	    } 
	    
	    throw 'Illegal function call';
	}
	
	if (sexp.type === DataTypes.Symbol) {
	    return Env.get(env, sexp.value);
	}
	
	return sexp;

    }
}