Improve completion in REPL (#343)

* Improve completion in REPL

- refine `get_context_object` to avoid throwing errors (eg: q.<TAB>)
- do not call `eval` in `get_context_object` to avoid throwing errors
  and reduce bloat caused by variable closures.
- support completion of directives

repl.js

@@ -551,51 +551,60 @@ import * as os from "os";
         cursor_pos = 0;
     }
 
-    function get_context_word(line, pos) {
+    function get_context_word(line, end) {
-        var s = "";
+        var pos = end;
-        while (pos > 0 && is_word(line[pos - 1])) {
+        while (pos > 0 && is_word(line[pos - 1]))
             pos--;
-            s = line[pos] + s;
+        return line.slice(pos, end);
-        }
-        return s;
     }
     function get_context_object(line, pos) {
-        var obj, base, c;
+        if (pos <= 0)
-        if (pos <= 0 || " ~!%^&*(-+={[|:;,<>?/".indexOf(line[pos - 1]) >= 0)
             return g;
-        if (pos >= 2 && line[pos - 1] === ".") {
+        var c = line[pos - 1];
+        if (pos === 1 && c === '\\')
+            return directives;
+        if ("'\"`@#)]}\\".indexOf(c) >= 0)
+            return void 0;
+        if (pos >= 2 && c === ".") {
             pos--;
-            obj = {};
             switch (c = line[pos - 1]) {
             case '\'':
             case '\"':
+            case '`':
                 return "a";
             case ']':
-                return [];
+                return [];  // incorrect for a[b].<TAB>
-            case '}':
-                return {};
             case '/':
                 return / /;
             default:
                 if (is_word(c)) {
-                    base = get_context_word(line, pos);
+                    var base = get_context_word(line, pos);
-                    if (["true", "false", "null", "this"].includes(base) || !isNaN(+base))
+                    var base_pos = pos - base.length;
-                        return eval(base);
+                    if (base === 'true' || base === 'false')
-                    // Check if `base` is a set of regexp flags
+                        return true;
-                    if (pos - base.length >= 3 && line[pos - base.length - 1] === '/')
+                    if (base === 'null')
-                        return new RegExp('', base);
+                        return null;
-                    obj = get_context_object(line, pos - base.length);
+                    if (base === 'this')
+                        return g;
+                    if (!isNaN(+base))  // number literal, incorrect for 1.<TAB>
+                        return 0;
+                    var obj = get_context_object(line, base_pos);
                     if (obj === null || obj === void 0)
                         return obj;
-                    if (obj === g && obj[base] === void 0)
+                    if (typeof obj[base] !== 'undefined')
-                        return eval(base);
-                    else
                         return obj[base];
+                    // Check if `base` is a set of regexp flags
+                    // TODO(chqrlie): this is incorrect for a/i<TAB>...
+                    // Should use colorizer to determine the token type
+                    if (base_pos >= 3 && line[base_pos - 1] === '/' && base.match(/^[dgimsuvy]+$/))
+                        return RegExp();
+                    // base is a local identifier, complete as generic object
+                }
+                break;
             }
             return {};
         }
-        }
+        return g;
-        return void 0;
     }
 
     function get_completions(line, pos) {
@@ -1044,6 +1053,10 @@ import * as os from "os";
                   "\\q          exit\n");
     }
 
+    var directives = Object.setPrototypeOf({
+        h: "h", help: "help", load: "load", x: "x", d: "d", t: "t",
+        clear: "clear", q: "q" }, null);
+
     function eval_and_print(expr) {
         var result;