dart-console: An interactive console for Dart

WARNING: This is a prototype and uses some hacky techniques under the hood. Performance may degrade during long-lived sessions and I wouldn't be surprised if this eventually breaks.

Example

>> print("Hello, dart!");
Hello, dart!
>> square(x) => x * x;
>> Math.sqrt(square(3) + square(4))
5.0
>> lives = 3;
>> die() {
{>   lives--;
{>   if (lives == 0) throw new Exception("Game over");
{> }
>> die();
>> die();
>> die();
Exception: Game over

Building (Linux/Mac)

You'll need:

• Dart SDK
• libreadline-dev
• Linux or Mac, g++ toolchain. (Windows is too hard, for now...)

Either edit build.sh to point to the SDK, or set the environment variable DART_SDK.

Building and running

./build.sh
bin/console

Limitations and workarounds

You can't "overwrite" a declared name.

>> foo() => 1;
>> foo() => 2;
Exception: 'console_declaration_3': Error: line 1 pos 1: 'foo' is already defined

Workaround: use variables instead of declarations

>> foo = () => 1;
>> foo = () => 2;
>> foo()
2

Global variables are not detected within declarations

>> bar() { x = 2; }
>> bar();
Exception: 'console_declaration_4': Error: line 1 pos 9: identifier 'x' is not declared in this scope

Workaround: initialize them in a statement beforehand

>> x = null;
>> bar() { x = 2; }
>> bar();
>> x
2

Workaround: use the VARIABLES map

>> bar() { VARIABLES['x'] = 2; }
>> bar();
>> x
2

Messages and behaviour are confusing when the console guesses your intent wrong

>> x() => 2 + 2 // missing semicolon
Closure
>> x
NoSuchMethodException : method not found: 'get:x'

Workaround: understand the types of input the console accepts

• Declarations: inserted at the top level.
  • Input ending in }
  • Lambda declarations like baz() => 42;
• Statements: wrapped in a method like _execute() {$code} and called
  • Input ending in ;
• Expressions: wrapped in a method like _execute() {return ($code);} and called
  • Everything else

Documentation

Not yet, poke around the code...

Tests

There are tests for the parsing and sandbox libraries, under test/. To run them:

./build.sh test

Legal stuff

Copyright 2012 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.