code: func jsonnet_evaluate_file(vmRef *C.struct_JsonnetVm, filename *C.char, e *C.int) *C.char {
  	f := C.GoString(filename)
  	data, err := ioutil.ReadFile(f)
  	if err != nil {
  		*e = 1
  		// TODO(sbarzowski) make sure that it's ok allocation-wise
  		return C.CString(fmt.Sprintf("Failed to read input file: %s: %s", f, err.Error()))
  	} else {
  		return evaluateSnippet(vmRef, f, string(data), e)
  	}
  }
docs: //export jsonnet_evaluate_file