// eval part var evaluate = function(x, env) { if (Array.isArray(x)) { if (x[0] === 'if') { // if というキーワードだった場合 return String(evaluate(x[1], env)) !== 'false' ? evaluate(x[2], env) : evaluate(x[3], env); } else { // if ではない場合、今までどおりの処理を行う var exps = x.map(function(exp) {return evaluate(exp, env);}); var proc = exps.shift(); return proc.apply(null, exps); } } else { var y = env[x]; return y !== undefined ? y : x; } }; // library var globalEnv = { '+': function(a, b) {return a + b;}, '-': function(a, b) {return a - b;}, '*': function(a, b) {return a * b;}, '/': function(a, b) {return a / b;}, 'mod': function(a, b) {return a % b;}, 'not': function(x) {return !x;}, '=': function(a, b) {return a === b;}, '>': function(a, b) {return a > b;}, '<': function(a, b) {return a < b;}, '<=': function(a, b) {return a <= b;}, '>=': function(a, b) {return a >= b;}, 'alert': function(a) {alert(a);}, 'console.log': function() {console.log(arguments);}, 'do': function() {} }; // usage evaluate(['do', ['console.log', 'A'], ['console.log', 'B']], globalEnv);