[0.4.0] Import as (#775)

* Add import "..." for Variable as OtherName

doc/site/modularity.markdown

@@ -42,6 +42,17 @@ if (thirsty) {
 }
 </pre>
 
+If you need to import a variable under a different name, you can use 
+`import "..." for Name as OtherName`. This looks up the top-level variable
+`Name` in *that* module, but declares a variable called `OtherName` in *this* module
+with its value.
+
+<pre class="snippet">
+import "liquids" for Water //Water is now taken
+import "beverages" for Coffee, Water as H2O, Tea
+// var water = H2O.new()
+</pre>
+
 If you want to load a module, but not bind any variables from it, you can omit
 the `for` clause:
 

doc/site/syntax.markdown

@@ -43,7 +43,7 @@ One way to get a quick feel for a language's style is to see what words it
 reserves. Here's what Wren has:
 
 <pre class="snippet">
-break class construct else false for foreign if import
+as break class construct else false for foreign if import
 in is null return static super this true var while
 </pre>
 

src/vm/wren_compiler.c

@@ -96,6 +96,7 @@ typedef enum
   TOKEN_FOREIGN,
   TOKEN_IF,
   TOKEN_IMPORT,
+  TOKEN_AS,
   TOKEN_IN,
   TOKEN_IS,
   TOKEN_NULL,
@@ -577,6 +578,7 @@ static Keyword keywords[] =
   {"foreign",   7, TOKEN_FOREIGN},
   {"if",        2, TOKEN_IF},
   {"import",    6, TOKEN_IMPORT},
+  {"as",        2, TOKEN_AS},
   {"in",        2, TOKEN_IN},
   {"is",        2, TOKEN_IS},
   {"null",      4, TOKEN_NULL},
@@ -2632,6 +2634,7 @@ GrammarRule rules[] =
   /* TOKEN_FOREIGN       */ UNUSED,
   /* TOKEN_IF            */ UNUSED,
   /* TOKEN_IMPORT        */ UNUSED,
+  /* TOKEN_AS            */ UNUSED,
   /* TOKEN_IN            */ UNUSED,
   /* TOKEN_IS            */ INFIX_OPERATOR(PREC_IS, "is"),
   /* TOKEN_NULL          */ PREFIX(null),
@@ -3378,17 +3381,38 @@ static void import(Compiler* compiler)
   do
   {
     ignoreNewlines(compiler);
-    int slot = declareNamedVariable(compiler);
     
-    // Define a string constant for the variable name.
-    int variableConstant = addConstant(compiler,
-        wrenNewStringLength(compiler->parser->vm,
-                            compiler->parser->previous.start,
-                            compiler->parser->previous.length));
+    consume(compiler, TOKEN_NAME, "Expect variable name.");
     
+    // We need to hold onto the source variable, 
+    // in order to reference it in the import later
+    Token sourceVariableToken = compiler->parser->previous;
+
+    // Define a string constant for the original variable name.
+    int sourceVariableConstant = addConstant(compiler,
+          wrenNewStringLength(compiler->parser->vm,
+                        sourceVariableToken.start,
+                        sourceVariableToken.length));
+
+    // Store the symbol we care about for the variable
+    int slot = -1;
+    if(match(compiler, TOKEN_AS))
+    {
+      //import "module" for Source as Dest
+      //Use 'Dest' as the name by declaring a new variable for it.
+      //This parses a name after the 'as' and defines it.
+      slot = declareNamedVariable(compiler);
+    }
+    else
+    {
+      //import "module" for Source
+      //Uses 'Source' as the name directly
+      slot = declareVariable(compiler, &sourceVariableToken);
+    }
+
     // Load the variable from the other module.
-    emitShortArg(compiler, CODE_IMPORT_VARIABLE, variableConstant);
-    
+    emitShortArg(compiler, CODE_IMPORT_VARIABLE, sourceVariableConstant);
+
     // Store the result in the variable here.
     defineVariable(compiler, slot);
   } while (match(compiler, TOKEN_COMMA));

test/language/module/import_as/import_as.wren

@@ -0,0 +1,11 @@
+var Module = "from here"
+var ValueC = "value C"
+import "./module" for ValueA, Module as Another, ValueB // expect: ran module
+import "./module" for ValueC as OtherC
+
+System.print(Module)  // expect: from here
+System.print(Another) // expect: from module
+System.print(ValueA)  // expect: module A
+System.print(ValueB)  // expect: module B
+System.print(ValueC)  // expect: value C
+System.print(OtherC)  // expect: module C

test/language/module/import_as/module.wren

@@ -0,0 +1,7 @@
+// nontest
+var Module = "from module"
+System.print("ran module")
+
+var ValueA = "module A"
+var ValueB = "module B"
+var ValueC = "module C"