Tab-completion in REPL based on module variables.

src/module/repl.wren

@@ -1,13 +1,6 @@
 import "meta" for Meta
 import "io" for Stdin
 
-class EscapeBracket {
-  static up { 65 }
-  static down { 66 }
-  static right { 67 }
-  static left { 68 }
-}
-
 class Repl {
   construct new() {
     _cursor = 0
@@ -19,7 +12,7 @@ class Repl {
 
   run() {
     Stdin.isRaw = true
-    refreshLine()
+    refreshLine(false)
 
     while (true) {
       var byte = Stdin.readByte()
@@ -32,7 +25,7 @@ class Repl {
         return
       } else if (byte == Chars.ctrlD) {
         // If the line is empty, Ctrl_D exits.
-        if (!_line.isEmpty) {
+        if (_line.isEmpty) {
           System.print()
           return
         }
@@ -43,6 +36,12 @@ class Repl {
         _cursor = _line.count
       } else if (byte == Chars.ctrlF) {
         cursorRight()
+      } else if (byte == Chars.tab) {
+        var completion = getCompletion()
+        if (completion != null) {
+          _line = _line + completion
+          _cursor = _line.count
+        }
       } else if (byte == Chars.ctrlK) {
         // Delete everything after the cursor.
         _line = _line[0..._cursor]
@@ -77,7 +76,7 @@ class Repl {
         System.print("Unhandled byte: %(byte)")
       }
 
-      refreshLine()
+      refreshLine(true)
     }
   }
 
@@ -157,6 +156,9 @@ class Repl {
   }
 
   executeInput() {
+    // Remove the completion hint.
+    refreshLine(false)
+
     // Add it to the history.
     _history.add(_line)
     _historyIndex = _history.count
@@ -191,12 +193,14 @@ class Repl {
     var fiber
     if (isStatement) {
       fiber = Fiber.new {
+        // TODO: Should evaluate in main module, not repl's own.
         Meta.eval(input)
       }
 
       var result = fiber.try()
       if (fiber.error == null) return
     } else {
+      // TODO: Should evaluate in main module, not repl's own.
       var function = Meta.compileExpression(input)
       if (function == null) return
 
@@ -204,6 +208,9 @@ class Repl {
       var result = fiber.try()
       if (fiber.error == null) {
         // TODO: Handle error in result.toString.
+        // TODO: Syntax color based on type? It might be nice to distinguish
+        // between string results versus stringified results. Otherwise, the
+        // user can't tell the difference between `true` and "true".
         System.print("%(Color.brightWhite)%(result)%(Color.none)")
         return
       }
@@ -229,7 +236,7 @@ class Repl {
     return tokens
   }
 
-  refreshLine() {
+  refreshLine(showCompletion) {
     // Erase the whole line.
     System.write("\x1b[2K")
 
@@ -247,9 +254,32 @@ class Repl {
       System.write(Color.none)
     }
 
+    if (showCompletion) {
+      var completion = getCompletion()
+      if (completion != null) {
+        System.write("%(Color.gray)%(completion)%(Color.none)")
+      }
+    }
+
     // Position the cursor.
     System.write("\r\x1b[%(2 + _cursor)C")
   }
+
+  /// Gets the best possible auto-completion for the current line, or null if
+  /// there is none. The completion is the remaining string to append to the
+  /// line, not the entire completed line.
+  getCompletion() {
+    if (_line.isEmpty) return null
+
+    // Only complete if the cursor is at the end.
+    if (_cursor != _line.count) return null
+
+    for (name in Meta.getModuleVariables("repl")) {
+      if (name.startsWith(_line)) {
+        return name[_line.count..-1]
+      }
+    }
+  }
 }
 
 /// ANSI color escape sequences.
@@ -351,6 +381,13 @@ class Chars {
   static isWhitespace(c) { c == space || c == tab || c == carriageReturn }
 }
 
+class EscapeBracket {
+  static up { 0x41 }
+  static down { 0x42 }
+  static right { 0x43 }
+  static left { 0x44 }
+}
+
 class Token {
   // Punctuators.
   static leftParen { "leftParen" }

src/module/repl.wren.inc

@@ -3,13 +3,6 @@ static const char* replModuleSource =
 "import \"meta\" for Meta\n"
 "import \"io\" for Stdin\n"
 "\n"
-"class EscapeBracket {\n"
-"  static up { 65 }\n"
-"  static down { 66 }\n"
-"  static right { 67 }\n"
-"  static left { 68 }\n"
-"}\n"
-"\n"
 "class Repl {\n"
 "  construct new() {\n"
 "    _cursor = 0\n"
@@ -21,7 +14,7 @@ static const char* replModuleSource =
 "\n"
 "  run() {\n"
 "    Stdin.isRaw = true\n"
-"    refreshLine()\n"
+"    refreshLine(false)\n"
 "\n"
 "    while (true) {\n"
 "      var byte = Stdin.readByte()\n"
@@ -34,7 +27,7 @@ static const char* replModuleSource =
 "        return\n"
 "      } else if (byte == Chars.ctrlD) {\n"
 "        // If the line is empty, Ctrl_D exits.\n"
-"        if (!_line.isEmpty) {\n"
+"        if (_line.isEmpty) {\n"
 "          System.print()\n"
 "          return\n"
 "        }\n"
@@ -45,6 +38,12 @@ static const char* replModuleSource =
 "        _cursor = _line.count\n"
 "      } else if (byte == Chars.ctrlF) {\n"
 "        cursorRight()\n"
+"      } else if (byte == Chars.tab) {\n"
+"        var completion = getCompletion()\n"
+"        if (completion != null) {\n"
+"          _line = _line + completion\n"
+"          _cursor = _line.count\n"
+"        }\n"
 "      } else if (byte == Chars.ctrlK) {\n"
 "        // Delete everything after the cursor.\n"
 "        _line = _line[0..._cursor]\n"
@@ -73,14 +72,13 @@ static const char* replModuleSource =
 "        // TODO: Ctrl-T to swap chars.\n"
 "        // TODO: ESC H and F to move to beginning and end of line. (Both ESC\n"
 "        // [ and ESC 0 sequences?)\n"
-"        // TODO: Ctrl-L clear screen.\n"
 "        // TODO: Ctrl-W delete previous word.\n"
 "        // TODO: Completion.\n"
 "        // TODO: Other shortcuts?\n"
 "        System.print(\"Unhandled byte: %(byte)\")\n"
 "      }\n"
 "\n"
-"      refreshLine()\n"
+"      refreshLine(true)\n"
 "    }\n"
 "  }\n"
 "\n"
@@ -160,6 +158,9 @@ static const char* replModuleSource =
 "  }\n"
 "\n"
 "  executeInput() {\n"
+"    // Remove the completion hint.\n"
+"    refreshLine(false)\n"
+"\n"
 "    // Add it to the history.\n"
 "    _history.add(_line)\n"
 "    _historyIndex = _history.count\n"
@@ -194,12 +195,14 @@ static const char* replModuleSource =
 "    var fiber\n"
 "    if (isStatement) {\n"
 "      fiber = Fiber.new {\n"
+"        // TODO: Should evaluate in main module, not repl's own.\n"
 "        Meta.eval(input)\n"
 "      }\n"
 "\n"
 "      var result = fiber.try()\n"
 "      if (fiber.error == null) return\n"
 "    } else {\n"
+"      // TODO: Should evaluate in main module, not repl's own.\n"
 "      var function = Meta.compileExpression(input)\n"
 "      if (function == null) return\n"
 "\n"
@@ -207,6 +210,9 @@ static const char* replModuleSource =
 "      var result = fiber.try()\n"
 "      if (fiber.error == null) {\n"
 "        // TODO: Handle error in result.toString.\n"
+"        // TODO: Syntax color based on type? It might be nice to distinguish\n"
+"        // between string results versus stringified results. Otherwise, the\n"
+"        // user can't tell the difference between `true` and \"true\".\n"
 "        System.print(\"%(Color.brightWhite)%(result)%(Color.none)\")\n"
 "        return\n"
 "      }\n"
@@ -232,7 +238,7 @@ static const char* replModuleSource =
 "    return tokens\n"
 "  }\n"
 "\n"
-"  refreshLine() {\n"
+"  refreshLine(showCompletion) {\n"
 "    // Erase the whole line.\n"
 "    System.write(\"\x1b[2K\")\n"
 "\n"
@@ -250,9 +256,32 @@ static const char* replModuleSource =
 "      System.write(Color.none)\n"
 "    }\n"
 "\n"
+"    if (showCompletion) {\n"
+"      var completion = getCompletion()\n"
+"      if (completion != null) {\n"
+"        System.write(\"%(Color.gray)%(completion)%(Color.none)\")\n"
+"      }\n"
+"    }\n"
+"\n"
 "    // Position the cursor.\n"
 "    System.write(\"\r\x1b[%(2 + _cursor)C\")\n"
 "  }\n"
+"\n"
+"  /// Gets the best possible auto-completion for the current line, or null if\n"
+"  /// there is none. The completion is the remaining string to append to the\n"
+"  /// line, not the entire completed line.\n"
+"  getCompletion() {\n"
+"    if (_line.isEmpty) return null\n"
+"\n"
+"    // Only complete if the cursor is at the end.\n"
+"    if (_cursor != _line.count) return null\n"
+"\n"
+"    for (name in Meta.getModuleVariables(\"repl\")) {\n"
+"      if (name.startsWith(_line)) {\n"
+"        return name[_line.count..-1]\n"
+"      }\n"
+"    }\n"
+"  }\n"
 "}\n"
 "\n"
 "/// ANSI color escape sequences.\n"
@@ -354,6 +383,13 @@ static const char* replModuleSource =
 "  static isWhitespace(c) { c == space || c == tab || c == carriageReturn }\n"
 "}\n"
 "\n"
+"class EscapeBracket {\n"
+"  static up { 0x41 }\n"
+"  static down { 0x42 }\n"
+"  static right { 0x43 }\n"
+"  static left { 0x44 }\n"
+"}\n"
+"\n"
 "class Token {\n"
 "  // Punctuators.\n"
 "  static leftParen { \"leftParen\" }\n"

src/optional/wren_opt_meta.c

@@ -36,6 +36,34 @@ void metaCompile(WrenVM* vm)
   }
 }
 
+void metaGetModuleVariables(WrenVM* vm) {
+  wrenEnsureSlots(vm, 3);
+  
+  Value moduleValue = wrenMapGet(vm->modules, vm->apiStack[1]);
+  if (IS_UNDEFINED(moduleValue))
+  {
+    vm->apiStack[0] = NULL_VAL;
+    return;
+  }
+    
+  ObjModule* module = AS_MODULE(moduleValue);  
+  ObjList* names = wrenNewList(vm, module->variableNames.count);
+  vm->apiStack[0] = OBJ_VAL(names);
+
+  // Initialize the elements to null in case a collection happens when we
+  // allocate the strings below.
+  for (int i = 0; i < names->elements.count; i++)
+  {
+    names->elements.data[i] = NULL_VAL;
+  }
+  
+  for (int i = 0; i < names->elements.count; i++)
+  {
+    String* name = &module->variableNames.data[i];
+    names->elements.data[i] = wrenNewString(vm, name->buffer, name->length);
+  }
+}
+
 const char* wrenMetaSource()
 {
   return metaModuleSource;
@@ -49,9 +77,19 @@ WrenForeignMethodFn wrenMetaBindForeignMethod(WrenVM* vm,
   // There is only one foreign method in the meta module.
   ASSERT(strcmp(className, "Meta") == 0, "Should be in Meta class.");
   ASSERT(isStatic, "Should be static.");
-  ASSERT(strcmp(signature, "compile_(_,_,_)") == 0, "Should be compile method.");
   
-  return metaCompile;
+  if (strcmp(signature, "compile_(_,_,_)") == 0)
+  {
+    return metaCompile;
+  }
+  
+  if (strcmp(signature, "getModuleVariables_(_)") == 0)
+  {
+    return metaGetModuleVariables;
+  }
+  
+  ASSERT(false, "Unknown method.");
+  return NULL;
 }
 
 #endif

src/optional/wren_opt_meta.wren

@@ -1,4 +1,12 @@
 class Meta {
+  static getModuleVariables(module) {
+    if (!(module is String)) Fiber.abort("Module name must be a string.")
+    var result = getModuleVariables_(module)
+    if (result != null) return result
+
+    Fiber.abort("Could not find a module named '%(module)'.")
+  }
+
   static eval(source) {
     if (!(source is String)) Fiber.abort("Source code must be a string.")
 
@@ -15,4 +23,5 @@ class Meta {
   }
 
   foreign static compile_(source, isExpression, printErrors)
+  foreign static getModuleVariables_(module)
 }

src/optional/wren_opt_meta.wren.inc

@@ -1,6 +1,14 @@
 // Generated automatically from src/optional/wren_opt_meta.wren. Do not edit.
 static const char* metaModuleSource =
 "class Meta {\n"
+"  static getModuleVariables(module) {\n"
+"    if (!(module is String)) Fiber.abort(\"Module name must be a string.\")\n"
+"    var result = getModuleVariables_(module)\n"
+"    if (result != null) return result\n"
+"\n"
+"    Fiber.abort(\"Could not find a module named '%(module)'.\")\n"
+"  }\n"
+"\n"
 "  static eval(source) {\n"
 "    if (!(source is String)) Fiber.abort(\"Source code must be a string.\")\n"
 "\n"
@@ -17,4 +25,5 @@ static const char* metaModuleSource =
 "  }\n"
 "\n"
 "  foreign static compile_(source, isExpression, printErrors)\n"
+"  foreign static getModuleVariables_(module)\n"
 "}\n";

test/meta/get_module_variables.wren

@@ -0,0 +1,17 @@
+import "meta" for Meta
+
+var variables = Meta.getModuleVariables("main")
+
+// Includes implicitly imported core stuff.
+System.print(variables.contains("Object")) // expect: true
+System.print(variables.contains("Bool")) // expect: true
+
+// Includes top level variables.
+System.print(variables.contains("variables")) // expect: true
+
+// Even ones declared later.
+System.print(variables.contains("later")) // expect: true
+
+var later = "values"
+
+System.print(variables.contains("unknown")) // expect: false

test/meta/get_module_variables_not_string.wren

@@ -0,0 +1,3 @@
+import "meta" for Meta
+
+Meta.getModuleVariables(123) // expect runtime error: Module name must be a string.

test/meta/get_module_variables_unknown_module.wren

@@ -0,0 +1,3 @@
+import "meta" for Meta
+
+Meta.getModuleVariables("unknown") // expect runtime error: Could not find a module named 'unknown'.