Add some failing tests for looping on the n flag.

eg/atari2600/build.sh

@@ -6,4 +6,5 @@ if [ "x$COMPARE" != "x" ]; then
   dcc6502 -o 0xf000 -m 200 smiley.bin > smiley.bin.disasm.txt
   dcc6502 -o 0xf000 -m 200 smiley-60p.bin > smiley-60p.bin.disasm.txt
   paste smiley.bin.disasm.txt smiley-60p.bin.disasm.txt | pr -t -e24
+  #diff -ru smiley.bin.disasm.txt smiley-60p.bin.disasm.txt
 fi

tests/SixtyPical Analysis.md

@@ -1669,6 +1669,18 @@ The body of `repeat forever` can be empty.
     | }
     = ok
 
+While `repeat` is most often used with `z`, it can also be used with `n`.
+
+    | routine main
+    |   outputs y, n, z
+    | {
+    |     ld y, 15
+    |     repeat {
+    |         dec y
+    |     } until n
+    | }
+    = ok
+
 ### for ###
 
 Basic "open-faced for" loop.  We'll start with the "upto" variant.

tests/SixtyPical Compilation.md

@@ -357,7 +357,7 @@ Compiling `if` without `else`.
     = $0813   LDY #$01
     = $0815   RTS
 
-Compiling `repeat`.
+Compiling `repeat ... until z`.
 
     | routine main
     |   trashes a, y, z, n, c
@@ -376,7 +376,7 @@ Compiling `repeat`.
     = $0813   BNE $080F
     = $0815   RTS
 
-Compiling `repeat until not`.
+Compiling `repeat ... until not z`.
 
     | routine main
     |   trashes a, y, z, n, c
@@ -395,6 +395,40 @@ Compiling `repeat until not`.
     = $0813   BEQ $080F
     = $0815   RTS
 
+Compiling `repeat ... until n`.
+
+    | routine main
+    |   trashes a, y, z, n, c
+    | {
+    |     ld y, 65
+    |     repeat {
+    |         ld a, y
+    |         dec y
+    |     } until n
+    | }
+    = $080D   LDY #$41
+    = $080F   TYA
+    = $0810   DEY
+    = $0811   BPL $080F
+    = $0813   RTS
+
+Compiling `repeat ... until not n`.
+
+    | routine main
+    |   trashes a, y, z, n, c
+    | {
+    |     ld y, 65
+    |     repeat {
+    |         ld a, y
+    |         inc y
+    |     } until not n
+    | }
+    = $080D   LDY #$41
+    = $080F   TYA
+    = $0810   INY
+    = $0811   BMI $080F
+    = $0813   RTS
+
 Compiling `repeat forever`.
 
     | routine main