restore the sharing of sequences. Shrinks the grammar by ~45%

src/runtime/c/pgf/writer.h

@@ -44,7 +44,8 @@ public:
     void write_parg(ref<PgfPArg> linarg);
     void write_presult(ref<PgfPResult> linres);
     void write_symbol(PgfSymbol sym);
-    void write_seq(ref<Vector<PgfSymbol>> seq);
+    void write_seq(ref<PgfSequence> seq);
+    void write_seq_id(ref<ref<PgfSequence>> r) { write_len((*r)->seq_id); };
     void write_lin(ref<PgfConcrLin> lin);
     void write_printname(ref<PgfConcrPrintname> printname);
 
@@ -58,10 +59,11 @@ private:
 
     void write_text(ref<ref<PgfText>> r) { write_text(&(**r)); };
     void write_lparam(ref<ref<PgfLParam>> r) { write_lparam(*r); };
-    void write_seq(ref<ref<Vector<PgfSymbol>>> r) { write_seq(*r); };
     void write_symbol(ref<PgfSymbol> r) { write_symbol(*r); };
     void write_presult(ref<ref<PgfPResult>> r) { write_presult(*r); };
 
+	size_t next_seq_id;
+	
     FILE *out;
     ref<PgfAbstr> abstract;
 };