1 files changed, 74 insertions, 0 deletions
diff --git a/system/doc/extensions/funparse.erl b/system/doc/extensions/funparse.erl
new file mode 100644
index 0000000000..5e23c90df9
--- /dev/null
+++ b/system/doc/extensions/funparse.erl
@@ -0,0 +1,74 @@
+-module(funparse).
+-compile(export_all).
+-import(lists, [reverse/1]).
+
+%17
+%% > hof:parse([a,c]).
+%% {ok,{'and',{'or',1,{const,a}},{'or',1,{const,c}}}}
+%% > hof:parse([a,d]). 
+%% {ok,{'and',{'or',1,{const,a}},{'or',2,{const,d}}}}
+%% > hof:parse([b,c]).   
+%% {ok,{'and',{'or',2,{const,b}},{'or',1,{const,c}}}}
+%% > hof:parse([b,d]). 
+%% {ok,{'and',{'or',2,{const,b}},{'or',2,{const,d}}}}
+%% > hof:parse([a,b]).   
+%% fail
+%17
+
+%% Grammar = (a | b) & (c | d)
+
+%12
+parse(List) ->
+    (grammar())(List).
+%12
+
+%13
+grammar() ->
+    pand(
+         por(pconst(a), pconst(b)),
+         por(pconst(c), pconst(d))).
+%13
+
+%14
+pconst(X) ->
+    fun (T) ->
+       case T of
+           [X|T1] -> {ok, {const, X}, T1};
+           _      -> fail
+       end
+    end.
+%14
+
+%15
+por(P1, P2) ->
+    fun (T) ->
+        case P1(T) of
+            {ok, R, T1} -> 
+                {ok, {'or',1,R}, T1};
+            fail -> 
+                case P2(T) of
+                    {ok, R1, T1} ->
+                        {ok, {'or',2,R1}, T1};
+                    fail ->
+                        fail
+                end
+        end
+    end.
+%15
+
+%16
+pand(P1, P2) ->
+    fun (T) ->
+        case P1(T) of
+            {ok, R1, T1} ->
+                case P2(T1) of
+                    {ok, R2, T2} ->
+                        {ok, {'and', R1, R2}};
+                    fail ->
+                        fail
+                end;
+            fail ->
+                fail
+        end
+    end.
+%16