From 3ea6bacad9fd7b14d5454d6ea109f5de724fd690 Mon Sep 17 00:00:00 2001
From: Jed Barber <jjbarber@y7mail.com>
Date: Tue, 22 May 2012 09:22:33 +1000
Subject: Split the Object wrapping from the actual computation in the article
 commands

---
 Term.hs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

(limited to 'Term.hs')

diff --git a/Term.hs b/Term.hs
index 20c70ce..23fc5c5 100644
--- a/Term.hs
+++ b/Term.hs
@@ -1,5 +1,8 @@
 module Term (
     Term(..),
+    Substitution,
+
+    nullTerm,
 
     alphaEquiv,
     alphaConvert,
@@ -31,7 +34,8 @@ data Term = TVar { tVar :: Var }
           | TApp { tAppLeft :: Term
                  , tAppRight :: Term }
           | TAbs { tAbsVar :: Term
-                 , tAbsTerm :: Term } deriving (Ord)
+                 , tAbsTerm :: Term }
+          | TNull deriving (Ord)
 
 type Substitution = ( [(Name,Type)], [(Var,Term)] )
 
@@ -50,6 +54,10 @@ instance Eq Term where
 
 
 
+nullTerm :: Term
+nullTerm = TNull
+
+
 alphaEquiv :: Term -> Term -> Bool
 alphaEquiv a b =
     let equiv = \term1 term2 varmap1 varmap2 depth ->
-- 
cgit