I'm also a fan of namespacing variants, and I used it extensively on an OCaml representation of the SpiderMonkey AST. (Coincidentally, up until writing our own parser we were using pfff's JavaScript parser! Go pfff!). Anyway, here are some other useful things I found in OCaml along the way:
Without namespacing, you might be using mutually recursive type definitions like
type statement = ExpressionStatement of expression
and expression = FunctionExpression of statement list
to do this with modules you need to use recursive modules, like
module rec Statement : sig
type t = Expression of Expression.t
end = struct
type t = Expression of Expression.t
end
and Expression : sig
type t = Function of Statement.t list
end = struct
type t = Function of Statement.t list
end
One of the sucky things about recursive modules is that you cannot omit the signatures, however if your modules only include types then there is a shortcut that looks like
module rec Statement : sig
type t = Expression of Expression.t
end = Statement
and Expression : sig
type t = Function of Statement.t list
end = Expression
In OCaml 4.01, the compiler is smart enough to distinguish between constructors with the same name but a different type -- so those variants wouldn't even need to be polymorphic anymore. This also partially mitigates the need for 'namespacing' your variants.
One thing to consider though is the grepability of a codebase. By relying more on nested modules, module aliases, opens, local opens, then many constructors have more than one way to be written and it makes it harder for grep to find what you look for. Of course people should not use grep and instead rely on IDE or tools that understand deeply the programming language being edited ... which makes the problem I mentioned go away. But still it's nice to have the possibility to use simple tools like grep and that they would simply work.
Without namespacing, you might be using mutually recursive type definitions like
to do this with modules you need to use recursive modules, like One of the sucky things about recursive modules is that you cannot omit the signatures, however if your modules only include types then there is a shortcut that looks like Links: Big real world example: https://github.com/facebook/flow/blob/3a5b4040b7d2a648f97a06...Recursive module docs: http://caml.inria.fr/pub/docs/manual-ocaml-400/manual021.htm...