1 files changed, 41 insertions, 4 deletions
diff --git a/lib/util.ml b/lib/util.ml
index a8c25f7456..9fb0d48ee8 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -87,7 +87,17 @@ let matrix_transpose mat =
 
 let identity x = x
 
-let compose f g x = f (g x)
+(** Left-to-right function composition:
+    
+    [f1 %> f2] is [fun x -> f2 (f1 x)].
+
+    [f1 %> f2 %> f3] is [fun x -> f3 (f2 (f1 x))].
+
+    [f1 %> f2 %> f3 %> f4] is [fun x -> f4 (f3 (f2 (f1 x)))]
+
+    etc.
+*)
+let (%>) f g x = g (f x)
 
 let const x _ = x
 
@@ -124,11 +134,38 @@ let delayed_force f = f ()
 
 type ('a, 'b) union = ('a, 'b) CSig.union = Inl of 'a | Inr of 'b
 type 'a until = 'a CSig.until = Stop of 'a | Cont of 'a
+type ('a, 'b) eq = ('a, 'b) CSig.eq = Refl : ('a, 'a) eq
+
+module Union =
+struct
+  let map f g = function
+    | Inl a -> Inl (f a)
+    | Inr b -> Inr (g b)
+
+  (** Lifting equality onto union types. *)
+  let equal f g x y = match x, y with
+    | Inl x, Inl y -> f x y
+    | Inr x, Inr y -> g x y
+    | _, _ -> false
+
+  let fold_left f g a = function
+    | Inl y -> f a y
+    | Inr y -> g a y
+end
 
-let map_union f g = function
-  | Inl a -> Inl (f a)
-  | Inr b -> Inr (g b)
+let map_union = Union.map
 
 type iexn = Exninfo.iexn
 
 let iraise = Exninfo.iraise
+
+let open_utf8_file_in fname =
+  let is_bom s =
+    Int.equal (Char.code s.[0]) 0xEF &&
+    Int.equal (Char.code s.[1]) 0xBB &&
+    Int.equal (Char.code s.[2]) 0xBF
+  in
+  let in_chan = open_in fname in
+  let s = "   " in
+  if input in_chan s 0 3 < 3 || not (is_bom s) then seek_in in_chan 0;
+  in_chan