Add Undefined object

This adds the `Undefined` object from HPC-GAP. This should never be exposed to GAP-Level code.
hulpke · Feb 3, 2016 · d26aadd · d26aadd
1 parent 3c1b847
commit d26aadd
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Showing 2 changed files with 33 additions and 5 deletions.
diff --git a/src/bool.c b/src/bool.c
@@ -36,14 +36,13 @@
 #include        "lists.h"               /* generic lists                   */
 #include        "stringobj.h"              /* strings                         */
 
-#include "code.h"		/* coder                           */
-#include "hpc/thread.h"		/* threads			   */
-#include "hpc/tls.h"			/* thread-local storage		   */
+#include	"code.h"		/* coder                           */
+#include	"hpc/thread.h"		/* threads			   */
+#include	"hpc/tls.h"		/* thread-local storage		   */
 
 
 /****************************************************************************
 **
-
 *V  True  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  true value
 **
 **   'True' is the value 'true'.
@@ -78,10 +77,21 @@ Obj Fail;
 */
 Obj SuPeRfail;
 
-
 /****************************************************************************
 **
+*V  Undefined  . . . . . . . . . . . . . . . . . . . . . . . undefined value
+**
+**  'Undefined' is a special object that is used in lieu of (Obj) 0 in places
+**  where the kernel cannot handle a null reference easily. This object is
+**  never exposed to GAP code and only used within the kernel.
+*/
+Obj Undefined;
+
+
 
+
+/****************************************************************************
+**
 *F  TypeBool( <bool> )  . . . . . . . . . . . . . . . type of a boolean value
 **
 **  'TypeBool' returns the type of boolean values.
@@ -118,6 +128,9 @@ void PrintBool (
     else if ( bool == SuPeRfail ) {
         Pr( "SuPeRfail", 0L, 0L );
     }
+    else if ( bool == Undefined ) {
+        Pr( "Undefined", 0L, 0L );
+    }
     else {
         Pr( "<<very strange boolean value>>", 0L, 0L );
     }
@@ -403,6 +416,7 @@ static Int InitKernel (
     InitGlobalBag( &False, "src/bool.c:FALSE" );
     InitGlobalBag( &Fail,  "src/bool.c:FAIL"  );
     InitGlobalBag( &SuPeRfail,  "src/bool.c:SUPERFAIL"  );
+    InitGlobalBag( &Undefined,  "src/bool.c:UNDEFINED"  );
 
     /* install the saving functions                                       */
     SaveObjFuncs[ T_BOOL ] = SaveBool;
@@ -417,6 +431,7 @@ static Int InitKernel (
     EqFuncs[ T_BOOL ][ T_BOOL ] = EqBool;
     LtFuncs[ T_BOOL ][ T_BOOL ] = LtBool;
 
+    MakeBagTypePublic(T_BOOL);
     /* return success                                                      */
     return 0;
 }
@@ -451,6 +466,9 @@ static Int InitLibrary (
     AssGVar( gvar, SuPeRfail );
     MakeReadOnlyGVar(gvar);
 
+    /* Undefined is an internal value */
+    Undefined = NewBag( T_BOOL, 0 );
+
     /* make and install the 'RETURN_TRUE' function                         */
     tmp = NewFunctionC( "RETURN_TRUE", -1L, "arg", ReturnTrue1 );
     HDLR_FUNC( tmp, 1 ) = ReturnTrue1;

diff --git a/src/bool.h b/src/bool.h
@@ -51,6 +51,16 @@ extern Obj Fail;
 */
 extern Obj SuPeRfail;
 
+/****************************************************************************
+**
+*V  Undefined  . . . . . . . . . . . . . . . . . . . . . . . undefined value
+**
+**  'Undefined' is a special object that is used in lieu of (Obj) 0 in places
+**  where the kernel cannot handle a null reference easily. This object is
+**  never exposed to GAP code and only used within the kernel.
+*/
+extern Obj Undefined;
+
 
 /****************************************************************************
 **