From 6915188a461b455e7112634f7a72612a9c6de54d Mon Sep 17 00:00:00 2001
From: RayMorgan <rmorgan@zappos.com>
Date: Thu, 24 Sep 2009 18:56:37 -0700
Subject: [PATCH] Enhanced the repl library.

Now supports:
- command options: .help, .break, .clear, .exit
- local vars and global functions
- ability to print 0, false and ""
- when value is a function, prints [Function]
- when object is circular, prints [Circular Object] instead of throwing an error
---
 lib/repl.js | 174 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 156 insertions(+), 18 deletions(-)

diff --git a/lib/repl.js b/lib/repl.js
index 46b83b50b4..a8d8f2686c 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -1,37 +1,175 @@
 // A repl library that you can include in your own code to get a runtime
 // interface to your program. Just require("/repl.js").
 
+puts("Type '.help' for options.");
+
 node.stdio.open();
+node.stdio.addListener("data", readline);
 
 var buffered_cmd = '';
 var trimmer = /^\s*(.+)\s*$/m;
+var scopedVar = /^\s*var\s*([_\w\$]+)(.*)$/m;
+var scopeFunc = /^\s*function\s*([_\w\$]+)/;
 
 exports.prompt = "node> ";
-
-function displayPrompt () {
-  print(buffered_cmd.length ? '...   ' : exports.prompt);
-}
+exports.scope = {};
 
 displayPrompt();
 
-node.stdio.addListener("data", function (cmd) {
-  var matches = trimmer.exec(cmd);
 
-  if (matches && matches.length == 2) {
-    cmd = matches[1];
+/**
+ * The main REPL function. This is called everytime the user enters
+ * data on the command line.
+ */
+function readline (cmd) {
+  cmd = trimWhitespace(cmd);
+  
+  // Check to see if a REPL keyword was used. If it returns true,
+  // display next prompt and return.
+  if (parseREPLKeyword(cmd) === true) {
+    return;
+  }
+  
+  // The catchall for errors
+  try {
+    buffered_cmd += cmd;
+    // This try is for determining if the command is complete, or should
+    // continue onto the next line.
     try {
-      buffered_cmd += cmd;
-      try {
-        puts(JSON.stringify(eval(buffered_cmd)));
-        buffered_cmd = '';
-      } catch (e) { 
-        if (!(e instanceof SyntaxError)) 
-          throw e;
+      buffered_cmd = convertToScope(buffered_cmd);
+      
+      // Scope the readline with exports.scope to provide "local" vars
+      with (exports.scope) {
+        var ret = eval(buffered_cmd);
+        printValue(ret);
       }
-    } catch (e) {
-      puts('caught an exception: ' + e);
+        
       buffered_cmd = '';
+    } catch (e) {
+      if (!(e instanceof SyntaxError)) 
+        throw e;
     }
+  } catch (e) {
+    // On error: Print the error and clear the buffer
+    puts('caught an exception: ' + e);
+    buffered_cmd = '';
   }
+  
   displayPrompt();
-});
+}
+
+
+/**
+ * Used to display the prompt. 
+ */
+function displayPrompt () {
+  print(buffered_cmd.length ? '...   ' : exports.prompt);
+}
+
+/**
+ * Used to parse and execute the Node REPL commands.
+ * 
+ * @param {cmd} cmd The command entered to check
+ * @returns {Boolean} If true it means don't continue parsing the command 
+ */
+function parseREPLKeyword (cmd) {
+  switch (cmd) {
+  case ".break":
+    buffered_cmd = '';
+    displayPrompt();
+    return true;
+  case ".clear":
+    puts("Clearing Scope...");
+    buffered_cmd = '';
+    exports.scope = {};
+    displayPrompt();
+    return true;
+  case ".exit":
+    node.stdio.close();
+    return true;
+  case ".help":
+    puts(".break\tSometimes you get stuck in a place you can't get out... This will get you out.");
+    puts(".clear\tBreak, and also clear the local scope.");
+    puts(".exit\tExit the prompt");
+    puts(".help\tShow repl options");
+    displayPrompt();
+    return true;
+  }
+  return 0;
+}
+
+/**
+ * Trims Whitespace from a line.
+ * 
+ * @param {String} cmd The string to trim the whitespace from
+ * @returns {String} The trimmed string 
+ */
+function trimWhitespace (cmd) {
+  var matches = trimmer.exec(cmd);
+  if (matches && matches.length == 2) {
+    return matches[1];
+  }
+}
+
+/**
+ * Converts commands that use var and function <name>() to use the
+ * local exports.scope when evaled. This provides a local scope
+ * on the REPL.
+ * 
+ * @param {String} cmd The cmd to convert
+ * @returns {String} The converted command
+ */
+function convertToScope (cmd) {
+  var matches;
+  
+  // Replaces: var foo = "bar";  with: exports.scope.foo = bar;
+  matches = scopedVar.exec(cmd);
+  if (matches && matches.length == 3) {
+    return "exports.scope." + matches[1] + matches[2];
+  }
+  
+  // Replaces: function foo() {};  with: foo = function foo() {};
+  matches = scopeFunc.exec(buffered_cmd);
+  if (matches && matches.length == 2) {
+    return matches[1] + " = " + buffered_cmd;
+  }
+  
+  return cmd;
+}
+
+/**
+ * Echos the value of a value. Trys to print the value out
+ * in the best way possible given the different types.
+ * 
+ * @param {Object} value The object to print out
+ */
+function printValue (value) {
+  if (value === 0) {
+    puts("0");
+    return;
+  }
+  
+  if (value === false) {
+    puts("false");
+    return;
+  }
+  
+  if (value === "") {
+    puts('""');
+    return;
+  }
+  
+  if (typeof(value) == "function") {
+    puts("[Function]");
+    return;
+  }
+  
+  try {
+    puts(JSON.stringify(value));
+  } catch (e) {
+    if (e.message.search("circular"))
+      puts("[Circular Object]");
+    else
+      throw e;
+  }
+}