From 0156bf0da091dd2a773c08c2917c121bc86643bb Mon Sep 17 00:00:00 2001
From: Adam Chlipala <adam@chlipala.net>
Date: Fri, 19 Aug 2011 15:23:01 -0400
Subject: Basis.mkMonad

---
 lib/ur/basis.urs  | 5 +++++
 lib/ur/option.ur  | 6 ++++++
 lib/ur/option.urs | 2 ++
 3 files changed, 13 insertions(+)

(limited to 'lib')

diff --git a/lib/ur/basis.urs b/lib/ur/basis.urs
index ece4bfef..494eaa4b 100644
--- a/lib/ur/basis.urs
+++ b/lib/ur/basis.urs
@@ -126,6 +126,11 @@ val bind : m ::: (Type -> Type) -> t1 ::: Type -> t2 ::: Type
            -> m t1 -> (t1 -> m t2)
            -> m t2
 
+val mkMonad : m ::: (Type -> Type)
+              -> {Return : t ::: Type -> t -> m t,
+                  Bind : t1 ::: Type -> t2 ::: Type -> m t1 -> (t1 -> m t2) -> m t2}
+              -> monad m
+
 con transaction :: Type -> Type
 val transaction_monad : monad transaction
 
diff --git a/lib/ur/option.ur b/lib/ur/option.ur
index 0aa07a2d..5c89fc9d 100644
--- a/lib/ur/option.ur
+++ b/lib/ur/option.ur
@@ -1,5 +1,11 @@
 datatype t = datatype Basis.option
 
+val monad = mkMonad {Return = @@Some,
+                     Bind = fn [a] [b] (m1 : t a) (m2 : a -> t b) =>
+                               case m1 of
+                                   None => None
+                                 | Some v => m2 v}
+
 fun eq [a] (_ : eq a) =
     mkEq (fn x y =>
              case (x, y) of
diff --git a/lib/ur/option.urs b/lib/ur/option.urs
index 62687963..ba43613f 100644
--- a/lib/ur/option.urs
+++ b/lib/ur/option.urs
@@ -1,5 +1,7 @@
 datatype t = datatype Basis.option
 
+val monad : monad t
+
 val eq : a ::: Type -> eq a -> eq (t a)
 val ord : a ::: Type -> ord a -> ord (t a)
 
-- 
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