update runtime executable

src/runtime/pixwerx.cpp

@@ -14,6 +14,7 @@
 
 #include <iostream>
 #include <fstream>
+#include <sstream>
 
 int main(int argc,const char** argv) {
 
@@ -24,19 +25,36 @@ int main(int argc,const char** argv) {
 
     argagg::parser_results args;
 
+    std::ostringstream usage;
+    usage
+            << "pixwerx rendering engine\n"
+            << '\n'
+            << "Usage: " << argv[0] << " [--help] [--file filename.lua]\n"
+            << '\n';
+
+
     try {
 
         args = argparser.parse(argc,argv);
 
     } catch (std::exception &e) {
 
-        std::cerr << e.what() << std::endl;
+
+
+        argagg::fmt_ostream help(std::cerr);
+
+        help << usage.str() << argparser << '\n'
+             << "Encountered exception while parsing arguments: " << e.what()
+             << '\n';
 
         return -1;
     }
 
     std::ifstream input;
 
+    // run a file
+    if (args["file"]) {
+
         input.open(args["file"].as<std::string>(),std::ifstream::in);
 
         if (!input.is_open()) {
@@ -55,4 +73,14 @@ int main(int argc,const char** argv) {
         pw::script s;
 
         return s.eval(sout.str().c_str());
+
+    // show help
+    } else if (args["help"]) {
+
+        argagg::fmt_ostream help(std::cerr);
+        help << usage.str() << argparser;
+
+    }
+
+    return 0;
 }