X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=code%2Fmonads.ml;h=7bb6894cda77723d028f216f38628a1c012c79ef;hp=2ba851b3bb904b7a9784a56e65178d02056f5ed3;hb=77808abfd2b5033980938ba74b82a733e36ed4e4;hpb=595509c48871d2cf8f420dc6cbb3668d21e85a61

diff --git a/code/monads.ml b/code/monads.ml
index 2ba851b3..7bb6894c 100644
--- a/code/monads.ml
+++ b/code/monads.ml
@@ -602,6 +602,11 @@ end) : sig
     val throw : err -> 'a m
     val catch : 'a m -> (err -> 'a m) -> 'a m
   end
+  (* ErrorT transformer when wrapped monad has plus, zero *)
+  module TP : functor (Wrapped : Monad.P) -> sig
+    include module type of T(Wrapped)
+    include Monad.PLUS with type 'a m := 'a m
+  end
   module T2 : functor (Wrapped : Monad.S2) -> sig
     type ('x,'a) result = ('x,'a) Wrapped.result
     type ('x,'a) result_exn = ('x,'a) Wrapped.result_exn
@@ -674,6 +679,15 @@ end = struct
       | Success _ -> Wrapped.unit t
       | Error e -> handler e)
   end
+  module TP(Wrapped : Monad.P) = struct
+    module TransP = struct
+      include T(Wrapped)
+      let plus u v = Wrapped.plus u v
+      let zero () = elevate (Wrapped.zero ())
+    end
+    include TransP
+    include (Monad.MakeDistrib(TransP) : Monad.PLUS with type 'a m := 'a m)
+  end
   module T2(Wrapped : Monad.S2) = struct
     module Trans = struct
       module Wrapped = Wrapped