Close #955 Change ^C handling in REPL

Press with text on the line: Cancels
Press on a bare line: Print a message
Press again on a bare line: Exit

doc/api/repl.markdown

@@ -77,9 +77,9 @@ The special variable `_` (underscore) contains the result of the last expression
     > _ += 1
     4
 
-The REPL provides access to any variables in the global scope. You can expose a variable
-to the REPL explicitly by assigning it to the `context` object associated with each
-`REPLServer`.  For example:
+The REPL provides access to any variables in the global scope. You can expose
+a variable to the REPL explicitly by assigning it to the `context` object
+associated with each `REPLServer`.  For example:
 
     // repl_test.js
     var repl = require("repl"),
@@ -97,7 +97,14 @@ There are a few special REPL commands:
 
   - `.break` - While inputting a multi-line expression, sometimes you get lost
     or just don't care about completing it. `.break` will start over.
-  - `.clear` - Resets the `context` object to an empty object and clears any multi-line expression.
+  - `.clear` - Resets the `context` object to an empty object and clears any
+    multi-line expression.
   - `.exit` - Close the I/O stream, which will cause the REPL to exit.
   - `.help` - Show this list of special commands.
 
+The following key combinations in the REPL have these special effects:
+
+  - `<ctrl>C` - Similar to the `.break` keyword.  Terminates the current
+    command.  Press twice on a blank line to forcibly exit.
+  - `<ctrl>D` - Similar to the `.exit` keyword.
+

lib/repl.js

@@ -101,17 +101,27 @@ function REPLServer(prompt, stream) {
 
   rli.setPrompt(self.prompt);
 
+  var sawSIGINT = false;
   rli.on('SIGINT', function() {
-    if (self.bufferedCommand && self.bufferedCommand.length > 0) {
-      rli.write('\n');
-      self.bufferedCommand = '';
-      self.displayPrompt();
-    } else {
-      rli.close();
+    if (sawSIGINT) {
+       rli.close();
+       process.exit();
     }
+    var bareInt = false;
+    if (!(self.bufferedCommand && self.bufferedCommand.length > 0) &&
+        rli.line.length === 0) {
+      rli.write('\n(^C again to quit)');
+      bareInt = true;
+    }
+    rli.line = '';
+    rli.write('\n');
+    self.bufferedCommand = '';
+    self.displayPrompt();
+    sawSIGINT = bareInt;
   });
 
   rli.addListener('line', function(cmd) {
+    sawSIGINT = false;
     var skipCatchall = false;
     cmd = trimWhitespace(cmd);