implemented nonExist

src/runtime/c/pgf/linearizer.cxx

@@ -310,10 +310,20 @@ void PgfLinearizer::free_ref(object x)
 PgfLinearizationOutput::PgfLinearizationOutput() : printer(NULL,0,NULL)
 {
     bind = true;
+    nonexist = false;
     capit = false;
     allcapit = false;
 }
 
+PgfText *PgfLinearizationOutput::get_text()
+{
+    if (nonexist) {
+        free(printer.get_text());
+        return NULL;
+    }
+    return printer.get_text();
+}
+
 void PgfLinearizationOutput::symbol_token(PgfText *tok)
 {
     if (!bind) {
@@ -375,6 +385,7 @@ void PgfLinearizationOutput::end_phrase(PgfText *cat, int fid, PgfText *ann, Pgf
 
 void PgfLinearizationOutput::symbol_ne()
 {
+    nonexist = true;
 }
 
 void PgfLinearizationOutput::symbol_bind()

src/runtime/c/pgf/linearizer.h

@@ -4,14 +4,15 @@
 class PGF_INTERNAL_DECL PgfLinearizationOutput : public PgfLinearizationOutputIface {
     PgfPrinter printer;
     bool bind;
+    bool nonexist;
     bool capit;
     bool allcapit;
 
 public:
     PgfLinearizationOutput();
 
-    PgfText *get_text() { return printer.get_text(); };
-    
+    PgfText *get_text();
+
 	virtual void symbol_token(PgfText *tok);
 	virtual void begin_phrase(PgfText *cat, int fid, PgfText *ann, PgfText *fun);
 	virtual void end_phrase(PgfText *cat, int fid, PgfText *ann, PgfText *fun);

src/runtime/c/pgf/printer.cxx

@@ -71,11 +71,13 @@ again: {
 
 PgfText *PgfPrinter::get_text()
 {
-    if (res == NULL) {
-        res = (PgfText*) malloc(sizeof(PgfText));
-        res->size = 0;
+    PgfText *tmp = res;
+    if (tmp == NULL) {
+        tmp = (PgfText*) malloc(sizeof(PgfText));
+        tmp->size = 0;
     }
-    return res;
+    res = NULL;
+    return tmp;
 }
 
 void PgfPrinter::flush_lambdas()

src/runtime/haskell/PGF2.hsc

@@ -584,7 +584,9 @@ linearize c e =
   bracket (newStablePtr e) freeStablePtr $ \c_e ->
   withForeignPtr marshaller $ \m ->
   bracket (withPgfExn "linearize" (pgf_linearize  (c_db c) c_revision c_e m)) free $ \c_text ->
-    peekText c_text
+    if c_text == nullPtr
+      then return ""
+      else peekText c_text
 
 -- | Generates all possible linearizations of an expression
 linearizeAll :: Concr -> Expr -> [String]