[lib] Split auxiliary libraries into Coq-specific and general.

Up to this point the `lib` directory contained two different library
archives, `clib.cma` and `lib.cma`, which a rough splitting between
Coq-specific libraries and general-purpose ones.

We know split the directory in two, as to make the distinction clear:

- `clib`: contains libraries that are not Coq specific and implement
  common data structures and programming patterns. These libraries
  could be eventually replace with external dependencies and the rest
  of the code base wouldn't notice much.

- `lib`: contains Coq-specific common libraries in widespread use
  along the codebase, but that are not considered part of other
  components. Examples are printing, error handling, or flags.

In some cases we have coupling due to utility files depending on Coq
specific flags, however this commit doesn't modify any files, but only
moves them around, further cleanup is welcome, as indeed a few files
in `lib` should likely be placed in `clib`.

Also note that `Deque` is not used ATM.

1 files changed, 94 insertions, 0 deletions

diff --git a/clib/monad.mli b/clib/monad.mli
new file mode 100644
index 000000000..7b0a3e600
--- /dev/null
+++ b/clib/monad.mli
@@ -0,0 +1,94 @@
+(***********************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team    *)
+(* <O___,, *        INRIA-Rocquencourt  &  LRI-CNRS-Orsay              *)
+(*   \VV/  *************************************************************)
+(*    //   *      This file is distributed under the terms of the      *)
+(*         *       GNU Lesser General Public License Version 2.1       *)
+(***********************************************************************)
+
+
+(** Combinators on monadic computations. *)
+
+
+(** A definition of monads, each of the combinators is used in the
+    [Make] functor. *)
+module type Def = sig
+
+  type +'a t
+  val return : 'a -> 'a t
+  val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
+  val (>>) : unit t -> 'a t -> 'a t
+  val map : ('a -> 'b) -> 'a t -> 'b t
+
+(** The monadic laws must hold:
+    - [(x>>=f)>>=g] = [x>>=fun x' -> (f x'>>=g)]
+    - [return a >>= f] = [f a]
+    - [x>>=return] = [x]
+
+    As well as the following identities:
+    - [x >> y] = [x >>= fun () -> y]
+    - [map f x] = [x >>= fun x' -> f x'] *)
+
+end
+
+
+(** List combinators *)
+module type ListS = sig
+
+  type 'a t
+
+  (** [List.map f l] maps [f] on the elements of [l] in left to right
+      order. *)
+  val map : ('a -> 'b t) -> 'a list -> 'b list t
+
+  (** [List.map f l] maps [f] on the elements of [l] in right to left
+      order. *)
+  val map_right : ('a -> 'b t) -> 'a list -> 'b list t
+
+  (** Like the regular [List.fold_right]. The monadic effects are
+      threaded right to left.
+
+      Note: many monads behave poorly with right-to-left order. For
+      instance a failure monad would still have to traverse the
+      whole list in order to fail and failure needs to be propagated
+      through the rest of the list in binds which are now
+      spurious. It is also the worst case for substitution monads
+      (aka free monads), exposing the quadratic behaviour.*)
+  val fold_right : ('a -> 'b -> 'b t) -> 'a list -> 'b -> 'b t
+
+  (** Like the regular [List.fold_left]. The monadic effects are
+      threaded left to right. It is tail-recursive if the [(>>=)]
+      operator calls its second argument in a tail position. *)
+  val fold_left : ('a -> 'b -> 'a t) -> 'a -> 'b list -> 'a t
+
+  (** Like the regular [List.iter]. The monadic effects are threaded
+      left to right. It is tail-recurisve if the [>>] operator calls
+      its second argument in a tail position. *)
+  val iter : ('a -> unit t) -> 'a list -> unit t
+
+  (** Like the regular {!CList.map_filter}. The monadic effects are
+      threaded left to right. *)
+  val map_filter : ('a -> 'b option t) -> 'a list -> 'b list t
+
+
+  (** {6 Two-list iterators} *)
+
+  (** [fold_left2 r f s l1 l2] behaves like {!fold_left} but acts
+      simultaneously on two lists. Runs [r] (presumably an
+      exception-raising computation) if both lists do not have the
+      same length. *)
+  val fold_left2 : 'a t ->
+    ('a -> 'b -> 'c -> 'a t) -> 'a -> 'b list -> 'c list -> 'a t
+
+end
+
+module type S = sig
+
+  include Def
+
+  module List : ListS with type 'a t := 'a t
+
+end
+
+(** Expands the monadic definition to extra combinators. *)
+module Make (M:Def) : S with type +'a t = 'a M.t