Expand monad_transformers re elevate, layering

[lambda.git] / code / monads.ml

diff --git a/code/monads.ml b/code/monads.ml
index e1865a4..b678a92 100644 (file)
--- a/code/monads.ml
+++ b/code/monads.ml
@@ -51,7 +51,8 @@
  * - http://www.grabmueller.de/martin/www/pub/Transformers.pdf
  * - http://en.wikibooks.org/wiki/Haskell/Monad_transformers
  *
- * Licensing: MIT (if that's compatible with the ghc sources).
+ * Licensing: MIT (if that's compatible with the ghc sources this is partly
+ * derived from)
  *)
 
 exception Undefined
@@ -73,7 +74,7 @@ module Util = struct
     in loop len []
   (* Dirty hack to be a default polymorphic zero.
    * To implement this cleanly, monads without a natural zero
-   * should always wrap themselves in an option layer (see Leaf_monad). *)
+   * should always wrap themselves in an option layer (see Tree_monad). *)
   let undef = Obj.magic (fun () -> raise Undefined)
 end
 
@@ -414,13 +415,6 @@ end = struct
   end
 end
 
-(*
-# LL.(run(plus (unit 1) (unit 2) >>= fun i -> plus (unit i) (unit(10*i)) ));;
-- : ('_a, int) LL.result = [[1; 10; 2; 20]]
-# LL.(run(plus (unit 1) (unit 2) >>= fun i -> elevate L.(plus (unit i) (unit(10*i)) )));;
-- : ('_a, int) LL.result = [[1; 2]; [1; 20]; [10; 2]; [10; 20]]
-*)
-
 
 (* must be parameterized on (struct type err = ... end) *)
 module Error_monad(Err : sig
@@ -515,26 +509,6 @@ module Failure = Error_monad(struct
   *)
 end)
 
-(*
-# EL.(run( plus (throw "bye") (unit 20) >>= fun i -> unit(i+10)));;
-- : int EL.result = [Failure.Error "bye"; Failure.Success 30]
-# LE.(run( plus (elevate (Failure.throw "bye")) (unit 20) >>= fun i -> unit(i+10)));;
-- : int LE.result = Failure.Error "bye"
-# EL.(run_exn( plus (throw "bye") (unit 20) >>= fun i -> unit(i+10)));;
-Exception: Failure "bye".
-# LE.(run_exn( plus (elevate (Failure.throw "bye")) (unit 20) >>= fun i -> unit(i+10)));;
-Exception: Failure "bye".
-
-# ES.(run( elevate (S.puts succ) >> throw "bye" >> elevate S.get >>= fun i -> unit(i+10) )) 0;;
-- : int Failure.error * S.store = (Failure.Error "bye", 1)
-# SE.(run( puts succ >> elevate (Failure.throw "bye") >> get >>= fun i -> unit(i+10) )) 0;;
-- : (int * S.store) Failure.result = Failure.Error "bye"
-# ES.(run_exn( elevate (S.puts succ) >> throw "bye" >> elevate S.get >>= fun i -> unit(i+10) )) 0;;
-Exception: Failure "bye".
-# SE.(run_exn( puts succ >> elevate (Failure.throw "bye") >> get >>= fun i -> unit(i+10) )) 0;;
-Exception: Failure "bye".
- *)
-
 
 (* must be parameterized on (struct type env = ... end) *)
 module Reader_monad(Env : sig type env end) : sig
@@ -666,6 +640,7 @@ end = struct
   end
 end
 
+
 (* State monad with different interface (structured store) *)
 module Ref_monad(V : sig
   type value
@@ -1013,14 +988,14 @@ end
  *)
 
 
-module Leaf_monad : sig
+module Tree_monad : sig
   (* We implement the type as `'a tree option` because it has a natural`plus`,
    * and the rest of the library expects that `plus` and `zero` will come together. *)
   type 'a tree = Leaf of 'a | Node of ('a tree * 'a tree)
   type ('x,'a) result = 'a tree option
   type ('x,'a) result_exn = 'a tree
   include Monad.S with type ('x,'a) result := ('x,'a) result and type ('x,'a) result_exn := ('x,'a) result_exn
-  (* LeafT transformer *)
+  (* TreeT transformer *)
   module T : functor (Wrapped : Monad.S) -> sig
     type ('x,'a) result = ('x,'a tree option) Wrapped.result
     type ('x,'a) result_exn = ('x,'a tree) Wrapped.result_exn
@@ -1094,7 +1069,7 @@ end
 module L = List_monad;;
 module R = Reader_monad(struct type env = int -> int end);;
 module S = State_monad(struct type store = int end);;
-module T = Leaf_monad;;
+module T = Tree_monad;;
 module LR = L.T(R);;
 module LS = L.T(S);;
 module TL = T.T(L);;
@@ -1104,7 +1079,7 @@ module C = Continuation_monad
 module TC = T.T(C);;
 
 
-print_endline "=== test Leaf(...).distribute ==================";;
+print_endline "=== test TreeT(...).distribute ==================";;
 
 let t1 = Some (T.Node (T.Node (T.Leaf 2, T.Leaf 3), T.Node (T.Leaf 5, T.Node (T.Leaf 7, T.Leaf 11))));;
 
@@ -1174,7 +1149,7 @@ LS.run (LS.distribute (fun i -> if i = -1 then S.get else if i < 0 then S.(puts
 - : S.store list * S.store = ([10; 0; 0; 1; 20], 1)
 *)
 
-print_endline "=== test Leaf(Continuation).distribute ==================";;
+print_endline "=== test TreeT(Continuation).distribute ==================";;
 
 let id : 'z. 'z -> 'z = fun x -> x