I have a C definition... unsigned long FPDF_GetLastError(); whose return values are... #define FPDF_ERR_SUCCESS 0 // No error. #define FPDF_ERR_UNKNOWN 1 // Unknown error. #define FPDF_ERR_FILE 2 // File not found or could not be opened. #define FPDF_ERR_FORMAT 3 // File not in PDF format or corrupted. #define FPDF_ERR_PASSWORD 4 // Password required or incorrect password. #define FPDF_ERR_SECURITY 5 // Unsupported security scheme. #define FPDF_ERR_PAGE 6 // Page not found or content error. I was thinking of turning those #define's into an FFIExternalEnumeration, but I was wondering if I'll hit some undefined behaviour with the underlying representation being a "long" rather than an "int" ? I do see here that C enumerations can be a range of types including "long" * https://stackoverflow.com/questions/7093360/c-sharp-enum-of-long-values but I'm not sure how it works in the Pharo context to know what the size underlying representation. cheers -ben