Here you can find the official X++ Programming Language reference guide : https://docs.microsoft.com/en-us/dynamicsax-2012/developer/x-language-programming-guide?redirectedfrom=MSDN
AX – D365FO – X++ Language reference Guide
Here you can find the official X++ Programming Language reference guide : https://docs.microsoft.com/en-us/dynamicsax-2012/developer/x-language-programming-guide?redirectedfrom=MSDN
AX / Dynamics 365 For Finance and Operations blog 