z80a: add ELSE,

blk.fs

@@ -300,11 +300,10 @@ CREATE lblnext 0 , ( stable ABI until set in B300 )
 : IFC, JRNC, FJR, ;
 : IFNC, JRC, FJR, ;
 : THEN,
-    DUP PC          ( l l pc )
-    -^ 1-           ( l off )
+    DUP PC ( l l pc ) -^ 1- ( l off )
     ( warning: l is a PC offset, not a mem addr! )
-    SWAP ORG @ + BIN( @ - ( off addr )
-    C! ;
+    SWAP ORG @ + BIN( @ - ( off addr ) C! ;
+: ELSE, JR, FJR, SWAP THEN, ;
 ( ----- 027 )
 : FWR BSET 0 C, ;
 : FSET @ THEN, ;

doc/asm.txt

@@ -87,6 +87,11 @@ the opposite condition is met, a relative jump is made to
 THEN,'s PC. For example, if you have IFZ, a jump is made when
 Z is unset.
 
+There can be an ELSE, in the middle of an IF, and THEN,. When
+present, IF, jumps to it when the condition is unmet. When the
+condition is met, upon reaching the ELSE, we unconditionally
+jump to the THEN,.
+
 On the BEGIN,..AGAIN, side, it's a bit different. You start
 with your BEGIN, instruction, and then later you issue a
 JRxx, instr followed by AGAIN,. Exactly like you would do
@@ -96,7 +101,7 @@ On top of that, you have the very nice BREAK, instruction,
 which must also be preceded by a JRxx, and will jump to the
 PC following the next AGAIN,. Examples:
 
-IFZ, NOP, THEN,
+IFZ, NOP, ELSE, NOP, THEN,
 BEGIN, NOP, JR, AGAIN, ( unconditional )
 BEGIN, NOP, JRZ, AGAIN, ( conditional )
 BEGIN, NOP, JRZ, BREAK, JR, AGAIN, ( break off the loop )