From 7d46bccdfc7cbcaaaf1dd5a8abb90ab76d16712a Mon Sep 17 00:00:00 2001
From: Elliot Glaysher <erg@google.com>
Date: Fri, 29 Sep 2017 21:26:50 -0700
Subject: [PATCH] Change the interface for random numbers.

---
 gen/test.hoon     | 12 ++++----
 lib/new-hoon.hoon | 71 ++++++++++++++++++++++++++++-------------------
 2 files changed, 49 insertions(+), 34 deletions(-)

diff --git a/gen/test.hoon b/gen/test.hoon
index ea7a49f77..476393f2d 100644
--- a/gen/test.hoon
+++ b/gen/test.hoon
@@ -92,7 +92,9 @@
       |=  {min/@ max/@}
       |=  c/@uvJ
       ^-  @
-      (add min (~(rad og c) (sub max min)))
+      =+  gen=(random:new-hoon c)
+      =^  num  gen  (range:gen min max)
+      num
     ::
     ++  generate-map
       :>  generator which will produce a map with {count} random pairs.
@@ -106,8 +108,8 @@
       ^-  (map @ud @ud)
       ?:  =(i count)
         m
-      =^  first  gen  (rads:gen 100)
-      =^  second  gen  (rads:gen 100)
+      =^  first  gen  (range:gen 0 100)
+      =^  second  gen  (range:gen 0 100)
       $(m (insert:mp:new-hoon m first second), i +(i))
     ::
     ::  ||  %test
@@ -611,8 +613,8 @@
     |-
     ?:  =(i 40)
       %.y
-    =^  key  gen  (rads:gen 100)
-    =^  value  gen  (rads:gen 100)
+    =^  key  gen  (range:gen 0 100)
+    =^  value  gen  (range:gen 0 100)
     =.  a  %^  alter-with-key  a  key
       |=  {key/@ud current/(maybe @ud)}
       ^-  (maybe @ud)
diff --git a/lib/new-hoon.hoon b/lib/new-hoon.hoon
index 3d086eead..e12957e43 100644
--- a/lib/new-hoon.hoon
+++ b/lib/new-hoon.hoon
@@ -1432,38 +1432,51 @@
     ==
   --
 ++  random
-  :>  produces a core which produces random numbers.
-  ::  todo: think hard about whether this interface really makes any sense;
-  ::  this is marginally better than ++og for rads usage, but still isn't good.
+  :>    produces a core which produces random numbers.
+  :>
+  :>  random numbers are generated through repeated sha-256 operations.
+  :>
+  :>  this design forces implementation details to be hidden, forces users to
+  :>  go through =^. this should be less error prone for pulling out multiple
+  :>  random numbers, at the cost of making getting a single random number
+  :>  slightly more cumbersome.
+  :>
+  :>      =+  gen=(random eny)
+  :>      =^  first  gen  (range:gen 0 10)
+  :>      =^  second  gen  (range:gen 0 10)
   |=  a/@
-  ::  note: interior was copied verbatim from ++og.
-  |%
-  ++  rad                                               ::  random in range
-    |=  b/@  ^-  @
-    =+  c=(raw (met 0 b))
-    ?:((lth c b) c $(a +(a)))
+  =>  |%
+      ++  raw                                               ::  random bits
+        |=  b/@  ^-  @
+        %+  can
+          0
+        =+  c=(shas %og-a (mix b a))
+        |-  ^-  (list {@ @})
+        ?:  =(0 b)
+          ~
+        =+  d=(shas %og-b (mix b (mix a c)))
+        ?:  (lth b 256)
+          [[b (end 0 b d)] ~]
+        [[256 d] $(c d, b (sub b 256))]
+      ::
+      ++  rad                                               ::  random in range
+        |=  b/@  ^-  @
+        =+  c=(raw (met 0 b))
+        ?:((lth c b) c $(a +(a)))
+      --
+  ^?  |%
+  ++  range
+    :>  returns a random number in the range [start, end], and generator.
+    |=  {start/@ end/@}
+    ?:  (gte start end)
+      ~_(leaf+"invalid range" !!)
+    =+  offset=(sub end start)
+    =+  r=(rad offset)
+    [(add start r) +>.$(a (shas %og-s (mix a r)))]
   ::
-  ++  rads                                              ::  random continuation
+  ++  bits
+    :>  returns {b} bits in the range, and generator.
     |=  b/@
-    =+  r=(rad b)
-    [r +>.$(a (shas %og-s (mix a r)))]
-  ::
-  ++  raw                                               ::  random bits
-    ::  ~/  %raw
-    |=  b/@  ^-  @
-    %+  can
-      0
-    =+  c=(shas %og-a (mix b a))
-    |-  ^-  (list {@ @})
-    ?:  =(0 b)
-      ~
-    =+  d=(shas %og-b (mix b (mix a c)))
-    ?:  (lth b 256)
-      [[b (end 0 b d)] ~]
-    [[256 d] $(c d, b (sub b 256))]
-  ::
-  ++  raws                                              ::  random bits
-    |=  b/@                                             ::  continuation
     =+  r=(raw b)
     [r +>.$(a (shas %og-s (mix a r)))]
   --