> I disagree with that. Haskell is category theory as a language No it is really not. Haskell only really has one category of any import, typically denoted 'Ha

> I disagree with that. Haskell is category theory as a language No it is really not. Haskell only really has one category of any import, typically denoted 'Hask'. There is no builtin way to embed or express arbitrary categories in Haskell. It's not even clear what this would mean, given that Haskell only has one conception of arrow (the function type '->'). In fact, Haskell is so far removed from true category theory that we have to use a compiler plugin (CCC by Conal Elliot) to get anything approaching compilation to arbitrary categories. Haskell is based on the polymorphically typed lambda calculus. Some decades after its design, some people realized they could use some abstract algebra concepts to help structure programs. You can use these concepts in any language with a sufficiently expressive type system. It is not specific to Haskell