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A old text on AG with functorial approach is Demazure-Gabriel (Introduction to algebraic geometry and algebraic groups) :
http://books.google.it/books?id=RDKRyP00aoMC&printsec=frontcover&dq=Algebraic+groups,+demazure&source=bl&ots=bINVNX5u5x&sig=PA40Oq8LOQdfBZgci6hFtXM-HGA&hl=it&ei=nQbfTJiCDs-fOqKP4esO&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBsQ6AEwAA#v=onepage&q&f=false
