Check argument type in new Fn.

src/wren_compiler.c

@@ -1456,9 +1456,6 @@ static void methodCall(Compiler* compiler, Code instruction,
 
     Compiler fnCompiler;
     initCompiler(&fnCompiler, compiler->parser, compiler, true);
-
-    // TODO: Allow newline between '{' and '|'?
-
     fnCompiler.numParams = parameterList(&fnCompiler, NULL, NULL,
                                          TOKEN_PIPE, TOKEN_PIPE);
 
@@ -2561,8 +2558,6 @@ static void classDefinition(Compiler* compiler)
 
   // Compile the method definitions.
   consume(compiler, TOKEN_LEFT_BRACE, "Expect '{' after class declaration.");
-
-  // TODO: Should newline be required here?
   matchLine(compiler);
 
   while (!match(compiler, TOKEN_RIGHT_BRACE))

src/wren_core.c

@@ -308,7 +308,11 @@ DEF_NATIVE(fn_instantiate)
 
 DEF_NATIVE(fn_new)
 {
-  // TODO: Validate arg type.
+  if (!IS_FN(args[1]) && !IS_CLOSURE(args[1]))
+  {
+    RETURN_ERROR("Argument must be a function.");
+  }
+
   // The block argument is already a function, so just return it.
   RETURN_VAL(args[1]);
 }

test/function/new_with_wrong_argument_type.wren

@@ -0,0 +1 @@
+new Fn(3) // expect runtime error: Argument must be a function.