From 2eacde7f2cc224cc554f27b56956165229017f27 Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Wed, 6 Dec 2017 02:33:32 +0100
Subject: [PATCH] TreeExplorer: draft the filter operation

should be low hanging fruit now....
---
 src/lib/iter-tree-explorer.hpp            | 88 +++++++++++++++++++++++
 tests/library/iter-tree-explorer-test.cpp |  7 +-
 wiki/thinkPad.ichthyo.mm                  | 32 +++++++--
 3 files changed, 121 insertions(+), 6 deletions(-)

diff --git a/src/lib/iter-tree-explorer.hpp b/src/lib/iter-tree-explorer.hpp
index 41174c927..3cfaf7a30 100644
--- a/src/lib/iter-tree-explorer.hpp
+++ b/src/lib/iter-tree-explorer.hpp
@@ -644,6 +644,80 @@ namespace lib {
             return *treated_;
           }
       };
+    
+    
+    
+    /**
+     * @internal Decorator for TreeExplorer to filter elements based on a predicate.
+     * 
+     * @todo WIP 12/17 implement filter
+     */
+    template<class SRC, class FUN>
+    class Filter
+      : public SRC
+      {
+        static_assert(can_IterForEach<SRC>::value, "Lumiera Iterator required as source");
+        using _Traits = _BoundFunctorTraits<FUN,SRC>;
+        using Res = typename _Traits::Res;
+        static_assert(std::is_constructible<bool, Res>::value, "Functor must be a predicate");
+        
+        using FilterPredicate = typename _Traits::Functor;
+        
+        FilterPredicate trafo_;
+        
+      public:
+        
+        Filter() =default;
+        // inherited default copy operations
+        
+        Filter (SRC&& dataSrc, FUN&& filterFun)
+          : SRC{move (dataSrc)}
+          , trafo_{forward<FUN> (filterFun)}
+          { }
+        
+        
+        /** refresh state when other layers manipulate the source sequence */
+        void
+        expandChildren()
+          {
+            //////////////////////TODO trigger re-evaluation here...
+            SRC::expandChildren();
+          }
+        
+      public: /* === Iteration control API for IterableDecorator === */
+        
+        bool
+        checkPoint()  const
+          {
+            return false; //////////////TODO filter and pull here...
+          }
+        
+        typename SRC::reference
+        yield()  const
+          {
+            return *(*this);
+          }
+        
+        void
+        iterNext()
+          {
+            ++ srcIter();
+          }
+        
+      private:
+        SRC&
+        srcIter()  const
+          {
+            return unConst(*this);
+          }
+        
+        bool
+        pullFilter ()
+          {
+            ////////////////////////TODO while-not-filter iter
+            return false; //////////TODO return true if any result??
+          }
+      };
   }
   
   
@@ -742,6 +816,20 @@ namespace lib {
           return TreeExplorer<ResIter> (ResCore {move(*this), forward<FUN>(transformFunctor)});
         }
       
+      
+      /** @todo implement filter
+       */
+      template<class FUN>
+      auto
+      filter (FUN&& filterPredicate)
+        {
+          using ResCore = iter_explorer::Filter<SRC, FUN>;
+          using ResIter = typename _DecoratorTraits<ResCore>::SrcIter;
+          
+          return TreeExplorer<ResIter> (ResCore {move(*this), forward<FUN>(filterPredicate)});
+        }
+      
+      
     private:
     };
   
diff --git a/tests/library/iter-tree-explorer-test.cpp b/tests/library/iter-tree-explorer-test.cpp
index 76b67620b..e237a5316 100644
--- a/tests/library/iter-tree-explorer-test.cpp
+++ b/tests/library/iter-tree-explorer-test.cpp
@@ -625,7 +625,10 @@ namespace test{
       void
       verify_FilterIterator()
         {
-          UNIMPLEMENTED("preconfigured repeated depth-first expansion");
+          cout << materialise (
+                    treeExplore(CountDown{10})
+                      .filter([](uint j){ return j % 2; })
+                  ) << endl;
         }
       
       
@@ -635,7 +638,7 @@ namespace test{
       void
       verify_asIterSource()
         {
-          UNIMPLEMENTED("preconfigured repeated depth-first expansion");
+          UNIMPLEMENTED("package as IterSource");
         }
       
       
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 9437241a6..1daa0c387 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -5691,8 +5691,8 @@
 </node>
 </node>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511837279715" ID="ID_1694539348" MODIFIED="1511837456610" TEXT="filter-Operation">
-<icon BUILTIN="hourglass"/>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511837279715" ID="ID_1694539348" MODIFIED="1512523928755" TEXT="filter-Operation">
+<icon BUILTIN="pencil"/>
 <node CREATED="1511837285306" ID="ID_928417859" MODIFIED="1511837293629" TEXT="der Vollst&#xe4;ndigkeit halber">
 <node CREATED="1511837296921" ID="ID_151298846" MODIFIED="1511837304547" TEXT="ist zwar redundant zu den Itertools"/>
 <node CREATED="1511837305410" ID="ID_1979322634" MODIFIED="1511837324464" TEXT="treeExplorer k&#xf6;nnte Itertools abl&#xf6;sen">
@@ -5700,10 +5700,19 @@
 <icon BUILTIN="idea"/>
 </node>
 </node>
-<node CREATED="1511837329140" ID="ID_1963360740" MODIFIED="1511837374658" TEXT="sollte billig zu implementieren sein">
+<node COLOR="#338800" CREATED="1511837329140" ID="ID_1963360740" MODIFIED="1512523888392" TEXT="billige Implementierung nach Schema-F">
+<icon BUILTIN="button_ok"/>
 <node CREATED="1511837338643" ID="ID_1734683995" MODIFIED="1511837344590" TEXT="bestehende Dekorator-Technik"/>
 <node CREATED="1511837345226" ID="ID_991593174" MODIFIED="1511837351797" TEXT="bestehende Funktor-Argument-Traits"/>
 </node>
+<node CREATED="1512523892775" ID="ID_673112014" MODIFIED="1512523896362" TEXT="Knackpunkte">
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1512523897422" ID="ID_1007287631" MODIFIED="1512523916092" TEXT="pullFilter">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node CREATED="1512523905005" ID="ID_1286045611" MODIFIED="1512523921543" TEXT="wie &quot;ausgewertet&quot; merken?">
+<icon BUILTIN="help"/>
+</node>
+</node>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1512363846804" ID="ID_1346062807" MODIFIED="1512363878326" TEXT="auto-expand">
 <icon BUILTIN="hourglass"/>
@@ -6276,9 +6285,24 @@
 <icon BUILTIN="button_ok"/>
 </node>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511836579562" ID="ID_1718741335" MODIFIED="1511836583779" TEXT="verify_FilterIterator();">
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511836579562" ID="ID_1718741335" MODIFIED="1512523829719" TEXT="verify_FilterIterator();">
+<icon BUILTIN="pencil"/>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1512523719350" ID="ID_351021178" MODIFIED="1512523742972" TEXT="einfaches Pr&#xe4;dikat">
 <icon BUILTIN="flag-yellow"/>
 </node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1512523726885" ID="ID_282579718" MODIFIED="1512523741403" TEXT="konsumieren bis leer">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1512523773559" ID="ID_917494688" MODIFIED="1512523798076" TEXT="Pr&#xe4;dikat&lt;Core&gt;">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1512523783318" ID="ID_1808219280" MODIFIED="1512523797205" TEXT="Pr&#xe4;dikat&lt;Iter&gt; (generisch)">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1512523810946" ID="ID_461047497" MODIFIED="1512523821311" TEXT="ggfs mit expand()">
+<icon BUILTIN="help"/>
+</node>
+</node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511836589393" ID="ID_54165230" MODIFIED="1511836592073" TEXT="verify_asIterSource();">
 <icon BUILTIN="flag-yellow"/>
 </node>