*psil, pocket lisp interpreter

psil-test.js

var cx = new env;
console.log(leval(['set','a',42],cx));
console.log(leval('a',cx));
console.log(leval(['eq',42,'a'],cx));
console.log(leval(['quote',[1,2]],cx));
console.log(leval(['fst',['quote',[1,2]]],cx));
console.log(leval(['rst',['quote',[1,2]]],cx));
console.log(leval(['cons',1,['quote',[2,3]]],cx));
console.log(leval(['cond',['eq',1,2],42,43],cx));
console.log(leval(['atom',['quote',[1,2]]],cx));
console.log(leval(['set','second',['quote',['lambda',['x'],['fst',['rst','x']]]]],cx));
console.log(leval(['second',['quote',[1,2,3]]],cx));

psil.js

function extcx(ar,cx){
    return ar.reduce(function(o, kv){ o[kv[0]] = kv[1]; return o; },cx || {})
}
function zip(ar1, ar2){
    return ar1.reduce(function(ar, v1, i1){ if (ar2[i1]) ar.push([v1,ar2[i1]]); return ar; },[])
}
function atomp(a){ return !(typeof a in {object:0,array:0}) }
function lazyp(a){ return (a in {cond:0,quote:0,lambda:0}) }

function env(){
    var inst = this;
    inst.atom = function(a){ return atomp(a) };
    inst.set = function(as){ return inst[as[0]] = as[1] };
    inst.quote = function(as){ return as[0] };
    inst.fst = function(as){ return as[0][0] };
    inst.rst = function(as){ return as[0].slice(1) };
    inst.cons = function(as){ return [as[0]].concat(as[1]) };
    inst.eq = function(as){ return as[0] === as[1] };
    inst.cond = function(as,cx){ return leval(as[0],cx) ? leval(as[1],cx) : leval(as[2],cx) };
    return inst;
}

function apply(rf, as, cx){
    return rf in cx && cx[rf].call ? cx[rf].call(null, as, cx) : leval(cx[rf][2], extcx(zip(cx[rf][1], as), cx));                                                      
}

function leval(sx, cx){
    if (atomp(sx)) return sx in cx ? cx[sx] : sx;
    var rf = sx[0], as = sx.slice(1).map(function(a){ return lazyp(rf) ? a : leval(a, cx) });
    return apply(rf, as, cx);
}