The Monad Challenges: Jump start your understanding of monads • Hacker News Board

Post by Chinjut » Wed, Jan 20, 2016, 6:13 PM UTC

LukeHoersten wrote: post #9

mrcactu5 wrote: post #7

I found a math background is a disadvantage for learning Haskell, since most mathematicians don't really use a lot of category theory. Lately that is changing, http://math.stackexchange.com/questions/1617592/is-set-prime... There's a lot of confusion on how the math version of "functor" or "monad" maps to the CS definitions. I found this tutorial on Monads and Applicatives helpful http://adit.io/posts/2013-04-17-func…

Something that doesn't help the Math->CS understanding of Functors is, for example, that languages like C++ use "Functor" to mean other things (function pointer in this case).

The C++ use of the word "functor" goes back to the original use of the word "functor" by Rudolf Carnap (to mean something like a word which combines with other words as arguments to produce a full term; a word that acts function-like, basically).

Saunders Mac Lane took the word "functor" from Carnap and gave it a particular definition in category theory (when founding category theory with Samuel Eilenberg). The ML languages and Haskell use the word "functor" in reference to this category theory sense of the word.

But category theory is not actually where the word "functor" originated. So perhaps we shouldn't say that C++ got its use of the word wrong, but rather, that there were simply two independent paths of evolution of technical uses of the word since its original creation by Rudolf Carnap for use in philosophy of language.