Is there any book similar to "Halmos Naive Set Theory" in Category Theory? When I wanted to learn set theory in high school, I found Halmos Naive Set Theory  book very readable and understandable. But now, at university, I have been searching for a similar book in category theory, but I haven't found any book like that until now.  
What is your suggestion?
Thanks in advance.
 A: Right; at college level, before, especially, algebraic topology, you are probably best off with something like SPIVAK. Also available as a pdf is Mac Lane, written by one of those who invented category theory, as something of an outgrowth of homological algebra. The latter is probably intended for graduate students. Meanwhile, it would not be surprising if there were still other books, at various levels. Category theory has become indispensable  for, say, algebraic geometry.  
Some nice reviews for an introductory book: CONCEPTUAL  then, with common author Lawvere SETS 
A: Doing a Google search for
"naive category theory",
here  the first hit:
Fibered Categories and the Foundations of Naive Category Theory
www.jstor.org/stable/2273784
JSTOR
by J Bénabou - ‎1985 - ‎Cited by 191
OF NAIVE CATEGORY THEORY. JEAN BENABOU. 
Introduction. Any attempt to give "foundations", for category theory or any domain in mathematics, could ...
A: Leinster recently came out with a fantastic book
Basic Category Theory, Tom Leinster, 2014
It is shallow in terms of proofs but it is deep with examples. This really will help you understand category theory from whichever mathematics you may already know best.
