String diagrams are a way to describe morphisms (think functions) in monoidal categories. A construction using monoidal categories (or a slight generalisation)

String diagrams are a way to describe morphisms (think functions) in monoidal categories. A construction using monoidal categories (or a slight generalisation) can be used to give a categorical model for arrows. http://bentnib.org/arrows.pdf http://bentnib.org/arrows.pdf This gives rise to these diagrams: https://www.haskell.org/arrows/ https://www.haskell.org/arrows/