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When is a function polymorphic?
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Date: 2005-03-31 (12:55)
From: Fermin Reig <fermin.reig@c...>
Subject: Re: [Caml-list] When is a function polymorphic?
On Thu, 2005-03-31 at 13:04, Yaron Minsky wrote:
> On Thu, 31 Mar 2005 17:32:23 +0900 (JST), Jacques Garrigue
> > Is it so difficult to make the extra constructors explicit?
> I'd say there are two issues.  The first is that it really can be a
> pain for large variant types, particularly when the contents of those
> types are changing during development, and you don't want the function
> in question to depend on anything other than the particular variants
> being modified.
> [...]

In my code, I try to avoid catchall '_' and 'x' patterns when possible.
I end up with long 'or' patterns, such as

| (A _ | B _ | C _ | ...) -> ...

This style, while more verbose, has one advantage: if I later add a new
constructor to my type, the exhaustiveness analysis warns me of all
places where I should check. (In fact, this is most useful during
development, since that's when type definitions change.)

Regarding the typing of

# function Some x -> Some () | None -> None;;
# function Some x -> Some () | x -> x;;

both Haskell and SML do the same as Ocaml, but, unlike Ocaml, neither
gives a polymorphic type when using an 'as x' pattern.


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