Draft

quiver graph: directed multigraph, 有向伪图

quiver, loop arrows from and to the same vertex

object, vertex in a graph

from directed multigraph to categories

morphism, or arrow

identity morphism

composition of morphisms

There can be multiple different loops on one object, but one of them must be the identity morphism. Why?

endofunctor

Haskell languge is a category, Hask, with the Haskell language types as the objects and Haskelllangauge functions are morphisms.

'Hask' is a Cartesian closed category

ncategory

monoids for input and output in Haskell language
Topics

Haskell and WL

category theory and WL
References
 Bartosz Milewsk, "Category Theory for Programmers," 2014  2017, https://bartoszmilewski.com/2014/10/28/categorytheoryforprogrammersthepreface/.
 Eugenia Cheng's research papers on category theory
 'TheCatsters' Youtube channel
 Tom Leinster, "Basic Category Theory," 2016, arXiv:1612.09375v1 [math.CT]
 Tom Leinster's research papers