Add word ?DUP

blk/046

@@ -2,6 +2,7 @@ Parameter Stack
 
 DROP        a --
 DUP         a -- a a
+?DUP        DUP if a is nonzero
 OVER        a b -- a b a
 ROT         a b c -- b c a
 SWAP        a b -- b a
@@ -12,5 +13,4 @@ SWAP        a b -- b a
 'S          Returns current stack pointer, not counting the
             push it's making right now.
 S0          Returns address of PSP TOS. When PSP is empty,
-            'S == S0
-                                                        (cont.)
+            'S == S0                                    (cont.)

blk/154

@@ -3,7 +3,7 @@
   hit 0. )
 : ENDCASE
     BEGIN
-        DUP NOT IF DROP EXIT THEN
+        ?DUP NOT IF EXIT THEN
         [COMPILE] THEN
     AGAIN
 ; IMMEDIATE

blk/307

@@ -1,9 +1,13 @@
 ( a -- a a )
 CODE DUP
-    HL POPqq,       ( A )
-    chkPS,
-    HL PUSHqq,      ( A )
-    HL PUSHqq,      ( A )
+    HL POPqq, chkPS,
+    HL PUSHqq, HL PUSHqq,
+;CODE
+
+CODE ?DUP
+    HL POPqq, chkPS,
+    HL PUSHqq,
+    HLZ, IFNZ, HL PUSHqq, THEN,
 ;CODE
 
 ( a -- )

blk/357

@@ -5,12 +5,12 @@
         - SWAP EXIT                    ( 0-n f )
     THEN
     0 SWAP _pdacc                 ( a r f )
-    DUP IF 2DROP 0 EXIT THEN
-    BEGIN                         ( a r 0 )
-        DROP SWAP 1+              ( r a+1 )
+    ?DUP IF 2DROP 0 EXIT THEN
+    BEGIN                         ( a r )
+        SWAP 1+                   ( r a+1 )
         DUP C@                    ( r a c )
         ROT SWAP                  ( a r c )
         _pdacc                    ( a r f )
-    DUP UNTIL
+    ?DUP UNTIL
     1 =         ( a r f )
     ROT DROP    ( r f ) ;

blk/360

@@ -6,7 +6,7 @@
     0  ( a r )
     BEGIN
     SWAP C@+                            ( r a+1 c )
-    DUP NOT IF 2DROP 1 EXIT THEN        ( r, 1 )
+    ?DUP NOT IF DROP 1 EXIT THEN        ( r, 1 )
     _                                   ( r a n )
     DUP 0< IF ROT 2DROP 0 EXIT THEN     ( a 0 )
     ROT 16 * +                          ( a r*16+n )

blk/362

@@ -6,7 +6,7 @@
     0  ( a r )
     BEGIN
     SWAP C@+                               ( r a+1 c )
-    DUP NOT IF 2DROP 1 EXIT THEN           ( r 1 )
+    ?DUP NOT IF DROP 1 EXIT THEN           ( r 1 )
     _                                      ( r a n )
     DUP 0< IF ROT 2DROP 0 EXIT THEN        ( a 0 )
     ROT 2 * +                              ( a r*2+n )

blk/364

@@ -1,7 +1,7 @@
 : C<? 0x06 RAM+ @ ;
 : C<
     0x08 RAM+ @  ( 08 == C<* override )
-    DUP NOT IF DROP 0x0c RAM+ @ THEN  ( 0c == C<* )
+    ?DUP NOT IF 0x0c RAM+ @ THEN  ( 0c == C<* )
     EXECUTE
 ;
 : , H@ ! H@ 2+ HERE ! ;

blk/367

@@ -1,6 +1,6 @@
 : SCPY
     BEGIN     ( a )
         C@+   ( a+1 c )
-        DUP NOT IF 2DROP EXIT THEN
+        ?DUP NOT IF DROP EXIT THEN
         C,    ( a c )
     AGAIN ;

blk/370

@@ -4,7 +4,7 @@
     LIT< (wnf) FIND DROP EXECUTE
 ;
 : ROLL
-    DUP NOT IF EXIT THEN
+    ?DUP NOT IF EXIT THEN
     1+ DUP PICK          ( n val )
     SWAP 2 * (roll)      ( val )
     SWAP DROP

blk/381

@@ -1,6 +1,6 @@
 : EMIT
     ( 0x53==(emit) override )
-    0x53 RAM+ @ DUP IF EXECUTE ELSE DROP (emit) THEN ;
+    0x53 RAM+ @ ?DUP IF EXECUTE ELSE (emit) THEN ;
 : (print)
     BEGIN
         C@+      ( a+1 c )
@@ -10,6 +10,6 @@
     AGAIN ;
 : BS 8 EMIT ; : LF 10 EMIT ; : CR 13 EMIT ;
 : CRLF CR LF ; : SPC 32 EMIT ;
-: NL 0x0a RAM+ @ ( NLPTR ) DUP IF EXECUTE ELSE DROP CRLF THEN ;
+: NL 0x0a RAM+ @ ( NLPTR ) ?DUP IF EXECUTE ELSE CRLF THEN ;
 : (uflw) LIT" stack underflow" ERR ;
 : (wnf) (print) SPC LIT" word not found" ERR ;

blk/387

@@ -9,7 +9,7 @@
 
 : KEY
     85 RAM+ @ ( (key) override )
-    DUP IF EXECUTE ELSE DROP (key) THEN ;
+    ?DUP IF EXECUTE ELSE (key) THEN ;
 
 
 ( cont.: read one char into input buffer and returns whether we

blk/414

@@ -11,5 +11,5 @@
     DUP _shift? IF DROP 1 PS2_SHIFT C! (key) EXIT THEN
     ( ah, finally, we have a gentle run-of-the-mill KC )
     PS2_CODES PS2_SHIFT C@ IF 0x80 + THEN + C@
-    DUP NOT IF DROP (key) THEN ;
+    ?DUP NOT IF (key) THEN ;