This text differs from most other introductions to category theory in the calculational style of the proofs (especially in Chapter~\ref{ch:constructions} and Appendix~\ref{moreonadjointness}), the restriction to applications within algorithmics, and the omission of many additional concepts and facts that I consider not helpful in a first introduction to category theory.
@incollection{mmf92b
,author = "Fokkinga, M.M."
,booktitle = "Lecture Notes of the {STOP} 1992 {S}ummerschool on
{C}onstructive {A}lgorithmics"
,month = sep
,pages = "1--72 of Part 1"
,publisher = "University of Utrecht"
,title = "A Gentle Introduction to Category Theory --- the
calculational approach"
,year = "1992"
}