CLEANUP: Renaming "Util.compose" function to "%"

I propose to change the name of the "Util.compose" function to "%".

Reasons:

1. If one wants to express function composition,
   then the new name enables us to achieve this goal easier.

2. In "Batteries Included" they had made the same choice.

2 files changed, 16 insertions, 2 deletions

diff --git a/lib/util.ml b/lib/util.ml
index b67539918..0f79c10df 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -87,7 +87,13 @@ let matrix_transpose mat =
 
 let identity x = x
 
-let compose f g x = f (g x)
+(** Function composition: the mathematical [∘] operator.
+
+    So [g % f] is a synonym for [fun x -> g (f x)].
+
+    Also because [%] is right-associative, [h % g % f] means [fun x -> h (g (f x))].
+ *)
+let (%) f g x = f (g x)
 
 let const x _ = x
 
diff --git a/lib/util.mli b/lib/util.mli
index 7923c65a3..559874bb8 100644
--- a/lib/util.mli
+++ b/lib/util.mli
@@ -83,7 +83,15 @@ val matrix_transpose : 'a list list -> 'a list list
 (** {6 Functions. } *)
 
 val identity : 'a -> 'a
-val compose : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'b
+
+(** Function composition: the mathematical [∘] operator.
+
+    So [g % f] is a synonym for [fun x -> g (f x)].
+
+    Also because [%] is right-associative, [h % g % f] means [fun x -> h (g (f x))].
+*)
+val (%) : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'b
+
 val const : 'a -> 'b -> 'a
 val iterate : ('a -> 'a) -> int -> 'a -> 'a
 val repeat : int -> ('a -> unit) -> 'a -> unit