update ski_evaluators

diff --git a/code/ski_evaluator.hs b/code/ski_evaluator.hs
index 26f1c0e..348b216 100644 (file)
--- a/code/ski_evaluator.hs
+++ b/code/ski_evaluator.hs
@@ -1,24 +1,24 @@
-data Term = I | S | K | App Term Term deriving (Eq, Show)      
-                                                              
-skomega = (App (App (App S I) I) (App (App S I) I))                      
+data Term = I | S | K | App Term Term deriving (Eq, Show)
+
+skomega = (App (App (App S I) I) (App (App S I) I))
 test = (App (App K I) skomega)
-                                                              
-reduce_one_step :: Term -> Term                                      
-reduce_one_step t = case t of                                      
-  App I a -> a                                                      
-  App (App K a) b -> a                                              
-  App (App (App S a) b) c -> App (App a c) (App b c)                      
-  _ -> t                                                      
-                                                              
-is_redex :: Term -> Bool                                      
-is_redex t = not (t == reduce_one_step t)                      
-                                                              
-reduce :: Term -> Term                                              
-reduce t = case t of                                              
-  I -> I                                                      
-  K -> K                                                      
-  S -> S                                                      
-  App a b ->                                                       
-    let t' = App (reduce a) (reduce b) in                      
-      if (is_redex t') then reduce (reduce_one_step t')      
-                       else t'                                
+
+reduce_if_redex :: Term -> Term
+reduce_if_redex t = case t of
+  App I a -> a
+  App (App K a) b -> a
+  App (App (App S a) b) c -> App (App a c) (App b c)
+  _ -> t
+
+is_redex :: Term -> Bool
+is_redex t = not (t == reduce_if_redex t)
+
+reduce_try2 :: Term -> Term
+reduce_try2 t = case t of
+  I -> I
+  K -> K
+  S -> S
+  App a b ->
+    let t' = App (reduce_try2 a) (reduce_try2 b) in
+      if (is_redex t') then reduce_try2 (reduce_if_redex t')
+                       else t'

diff --git a/code/ski_evaluator.ml b/code/ski_evaluator.ml
index 4d6f9a1..15ee4a7 100644 (file)
--- a/code/ski_evaluator.ml
+++ b/code/ski_evaluator.ml
@@ -1,30 +1,32 @@
-type term = I | S | K | App of (term * term)                    
-                                                               
-let skomega = App (App (App (S,I), I), App (App (S,I), I))                
+type term = I | S | K | App of (term * term)
+
+let skomega = App (App (App (S,I), I), App (App (S,I), I))
 let test = App (App (K,I), skomega)
-                                                                      
-let reduce_one_step (t:term):term = match t with                    
-    App(I,a) -> a                                                    
-  | App(App(K,a),b) -> a                                             
-  | App(App(App(S,a),b),c) -> App(App(a,c),App(b,c))                       
-  | _ -> t                                                     
-                                                               
-let is_redex (t:term):bool = not (t = reduce_one_step t)        
-                                                                      
-let rec reduce (t:term):term = match t with                        
-    I -> I                                                     
-  | K -> K                                                     
-  | S -> S                                                     
-  | App (a, b) ->                                                   
-      let t' = App (reduce a, reduce b) in                      
-        if (is_redex t') then reduce (reduce_one_step t')     
-                         else t'                               
 
-let rec reduce_lazy (t:term):term = match t with                        
-    I -> I                                                     
-  | K -> K                                                     
-  | S -> S                                                     
-  | App (a, b) ->                                                   
-      let t' = App (reduce_lazy a, b) in                      
-        if (is_redex t') then reduce_lazy (reduce_one_step t')     
-                         else t'                               
+let reduce_if_redex (t:term):term = match t with
+  | App(I,a) -> a
+  | App(App(K,a),b) -> a
+  | App(App(App(S,a),b),c) -> App(App(a,c),App(b,c))
+  | _ -> t
+
+let is_redex (t:term):bool = not (t = reduce_if_redex t)
+
+let rec reduce_try2 (t:term):term = match t with
+  | I -> I
+  | K -> K
+  | S -> S
+  | App (a, b) ->
+      let t' = App (reduce_try2 a, reduce_try2 b) in
+      if (is_redex t') then let t'' = reduce_if_redex t'
+                            in reduce_try2 t''
+                       else t'
+
+let rec reduce_lazy (t:term):term = match t with
+  | I -> I
+  | K -> K
+  | S -> S
+  | App (a, b) ->
+      let t' = App (reduce_lazy a, b) in
+      if (is_redex t') then let t'' = reduce_if_redex t'
+                            in reduce_lazt t''
+                       else t'