1 files changed, 33 insertions, 2 deletions
diff --git a/gi/pyp-topics/src/contexts_corpus.hh b/gi/pyp-topics/src/contexts_corpus.hh
index e680cef5..bd0cd34c 100644
--- a/gi/pyp-topics/src/contexts_corpus.hh
+++ b/gi/pyp-topics/src/contexts_corpus.hh
@@ -11,6 +11,36 @@
 #include "contexts_lexer.h"
 #include "../../../decoder/dict.h"
 
+
+class BackoffGenerator {
+public:
+  virtual ContextsLexer::Context
+    operator()(const ContextsLexer::Context& c) = 0;
+
+protected:
+  ContextsLexer::Context strip_edges(const ContextsLexer::Context& c) {
+    if (c.size() <= 1) return ContextsLexer::Context();
+    assert(c.size() % 2 == 1);
+    return ContextsLexer::Context(c.begin() + 1, c.end() - 1);
+  }
+};
+
+class NullBackoffGenerator : public BackoffGenerator {
+  virtual ContextsLexer::Context
+    operator()(const ContextsLexer::Context&) 
+    { return ContextsLexer::Context(); }
+};
+
+class SimpleBackoffGenerator : public BackoffGenerator {
+  virtual ContextsLexer::Context
+    operator()(const ContextsLexer::Context& c) { 
+      if (c.size() <= 3)
+        return ContextsLexer::Context();
+      return strip_edges(c); 
+    }
+};
+
+
 ////////////////////////////////////////////////////////////////
 // ContextsCorpus
 ////////////////////////////////////////////////////////////////
@@ -22,10 +52,11 @@ public:
     typedef boost::ptr_vector<Document>::const_iterator const_iterator;
 
 public:
-    ContextsCorpus() {}
+    ContextsCorpus() : m_backoff(new TermBackoff) {}
     virtual ~ContextsCorpus() {}
 
-    unsigned read_contexts(const std::string &filename);
+    unsigned read_contexts(const std::string &filename, 
+                           BackoffGenerator* backoff_gen=0);
 
     TermBackoffPtr backoff_index() {
       return m_backoff;