Functor (English Wikipedia)

Analysis of information sources in references of the Wikipedia article "Functor" in English language version.

refsWebsite

Global rank English rank

3^rd place

low place

7,198^th place

2^nd place

books.google.com

Simmons (2011), Exercise 3.1.4. Simmons, Harold (2011), "Functors and natural transformations", An Introduction to Category Theory, pp. 72–107, doi:10.1017/CBO9780511863226.004, ISBN 978-1-107-01087-1
Popescu, Nicolae; Popescu, Liliana (1979). Theory of categories. Dordrecht: Springer. p. 12. ISBN 9789400995505. Retrieved 23 April 2016.

It's not entirely clear that Haskell datatypes truly form a category. See https://wiki.haskell.org/Hask for more details.
See https://wiki.haskell.org/Category_theory/Functor#Functors_in_Haskell for more information.