[ocaml] try a monad module type

coq/mathcomp/mathcomp2/_CoqProject

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+-I /media/julinusername/eins/gits/math-comp/mathcomp
+-R /media/julinusername/eins/gits/math-comp/mathcomp mathcomp
+
+-arg -w -arg -projection-no-head-constant
+-arg -w -arg -redundant-canonical-projection
+-arg -w -arg -notation-overridden
+-arg -w -arg +duplicate-clear
+-arg -w -arg +non-primitive-record
+-arg -w -arg +undeclared-scope
+-arg -w -arg +deprecated-hint-rewrite-without-locality
+-arg -w -arg -elpi.add-const-for-axiom-or-sectionvar

ocaml/monads.ml

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+(* https://cs3110.github.io/textbook/chapters/ds/monads.html *)
+
+module type Monad = sig
+  type 'a t
+  val return: 'a -> 'a t
+  val (>>=): 'a t -> ('a -> 'b t) -> 'b t
+end
+
+module Maybe : Monad = struct
+  type 'a t = 'a option
+  let return a = Some a
+  let (>>=) a f =
+    match a with
+    | None -> None
+    | Some a' -> f a'
+end