Randall L. Brukardt & Robert A. Duff 
Ada 2012 Reference Manual. Language and Standard Libraries [PDF ebook] 
International Standard ISO/IEC 8652/2012 (E)

The Ada 2012 Reference Manual is an enhanced version of the text of International Standard ISO/IEC 8652/2012(E) for the programming language Ada. The Ada 2012 Reference Manual combines all of the previous corrections of Technical Corrigendum 1 and Amendment 1 with changes and additions that improve the capabilities of the language and the reliability of programs written in the language. The Ada 2012 Reference Manual will replace the former versions as an indispensable working companion for anybody using Ada professionally or learning and studying the language systematically.