update example and simplify a bit

Makefile

@@ -0,0 +1,2 @@
+main: main.c
+	gcc -o $@ $^ $$(pkg-config --cflags --libs ruby)

Rakefile.rb

@@ -1,22 +0,0 @@
-require "rscons"
-
-WINDOWS_RUBY_PATH = "/cygdrive/c/Ruby193"
-
-task :default do
-  Rscons::Environment.new do |env|
-    if RUBY_PLATFORM =~ /cygwin/
-      env["CC"] = "i686-pc-mingw32-gcc"
-      env["CPPPATH"] += [
-        "#{WINDOWS_RUBY_PATH}/include/ruby-1.9.1",
-        "#{WINDOWS_RUBY_PATH}/include/ruby-1.9.1/i386-mingw32",
-      ]
-      env["LIBS"] += ["msvcrt-ruby191"]
-      env["LDFLAGS"] += ["-L#{WINDOWS_RUBY_PATH}/lib"]
-    else
-      env.parse_flags!("!pkg-config --cflags --libs ruby-1.9")
-    end
-    env["CFLAGS"] += ["-Wall"]
-    sources = Dir["*.c"]
-    env.Program("main", sources)
-  end
-end

main.c

@@ -1,39 +1,50 @@
 #include <stdio.h>
-#include "ruby.h"
+#include <ruby.h>
+#include <stdbool.h>
 
-RUBY_GLOBAL_SETUP
-
-static VALUE eval(const char * string)
+VALUE ruby_protect_eval_string_rescue(VALUE exception, VALUE exception_object)
 {
-    int state;
-    VALUE v = rb_eval_string_protect(string, &state);
-    if (state != 0)
-    {
-//        fprintf(stderr, "rb_eval_string_protect() returned state %d!\n", state);
-        VALUE e = rb_errinfo();
-        VALUE s = rb_funcall(e, rb_intern("message"), 0);
-        fprintf(stderr, "%s\n", StringValueCStr(s));
-        rb_set_errinfo(Qnil);
-    }
-    return v;
+    *(bool *)exception = true;
+    fprintf(stderr, "exception: %s\n",
+            rb_obj_classname(exception_object));
+    return Qnil;
 }
 
-int main(int argc, char *argv[])
+VALUE ruby_protect_eval_string(const char * ruby_expression, bool * exception)
 {
-    int _argc = 1;
-    char *_argv[] = {"main"};
-    char **_argv_p = &_argv[0];
-    ruby_sysinit(&_argc, &_argv_p);
+    *exception = false;
+    return rb_rescue(rb_eval_string, (VALUE)ruby_expression,
+            ruby_protect_eval_string_rescue, (VALUE)exception);
+}
+
+int main(int argc, char **argv)
+{
+    if (argc < 2)
+    {
+        fprintf(stderr, "Usage: %s <ruby-expression>\n", argv[0]);
+        return -1;
+    }
+    VALUE v = INT2FIX(0);
+    bool exception;
     {
         RUBY_INIT_STACK;
         ruby_init();
-        ruby_init_loadpath();
-        VALUE v = eval("3 + 8");
-        printf("v: %d\n", FIX2INT(v));
-        eval("yoda");
-        eval("File.open('out.txt', 'w') {|fh| fh.puts 'hello!'}");
-        eval("puts 'Hello, World!'");
-        ruby_finalize();
+        v = ruby_protect_eval_string(argv[1], &exception);
+    }
+    if (exception)
+    {
+        fprintf(stderr, "Exception!\n");
+    }
+    else
+    {
+        if (FIXNUM_P(v))
+        {
+            printf("Success! Result is %d\n", FIX2INT(v));
+        }
+        else
+        {
+            printf("Success! Non-Fixnum result\n");
+        }
     }
     return 0;
 }