OCaml's module system (and conventions associated with it) give a few advantages over Haskell.
- There are good conventions for naming and argument order (and named arguments!) so I don't have to memorize a bunch of different APIs. This is made possible by the module system. It could probably be solved in Haskell with better tooling.
- Modules allow you to, for lack of a better word, make your code more modular. Modules are essentially the same thing as what people use objects for in Java. They let you abstract implementation and program against a particular interface (i.e., a collection of types and values) easily in a way you can't really in Haskell.
- There are good conventions for naming and argument order (and named arguments!) so I don't have to memorize a bunch of different APIs. This is made possible by the module system. It could probably be solved in Haskell with better tooling.
- Modules allow you to, for lack of a better word, make your code more modular. Modules are essentially the same thing as what people use objects for in Java. They let you abstract implementation and program against a particular interface (i.e., a collection of types and values) easily in a way you can't really in Haskell.