Refactoring Challenge
I created this exercise for myself to push the limits of my refactoring abilities. I put it online because I enjoyed the exercise, and hope that others are similarly masochistic. It increased my confidence that refactoring can fix any code, no matter how bad. First, I needed a prime example of an incomprehensible knot of spaghetti code, not too large but not too small. Shouldn't be hard to find. Then I would refactor mercilessly and completely untangle it. The idea is similar to the "Obfuscated C++" column from C++ Report, except that instead of trying to comprehend the code, I would try to make it comprehensible.
While looking for such an example, a childhood memory came back
to me. About 20 years ago, when I was 13 or 14, I was mystified by a
program in a book of BASIC programs. It was 138 lines of mostly
The program is listed on the right. If you're afraid I might have made a typo, you can check the original scan of the page. There is at least one actual bug in the code!
I wrote my solution in Java.
(Don't cheat, but here it is for comparison).
It took me about 6 or 7 hours.
The first challenge is figuring out how to translate a zillion
I don't feel I refactored it all the way. I only took it far enough to understand it. (And I fixed at least one bug). While I was refactoring, I kept feeling that I should be adding unit tests, because each refactoring carries some risk of screwing up. But I couldn't think of any good tests. It could be that I am not familiar enough with adding unit tests after the fact. It seems to me that testable units appeared only at the end, when the code took on a level of comprehensibility that I was satisfied with. Notes on TRS80 Model I BASIC:

From "BASIC Computer Games, TRS80 Edition" by David H. Ahl, ©1979, page 3. 10 CLS: PRINT @ 412,"AMAZING" 20 PRINT @ 538,"COPYRIGHT BY" 30 PRINT @ 587,"CREATIVE COMPUTING MORRISTOWN, NEW JERSEY" 40 FOR II=1 TO 1500: NEXT 50 CLS: INPUT"WHAT ARE YOUR WIDTH AND LENGTH"; H,V 60 IF H<>1 AND V<>1 THEN 90 70 PRINT "MEANINGLESS DIMENSIONS. TRY AGAIN" 80 FOR A=1 TO 500: NEXT A: GOTO 50 90 PRINT @ 522,"PRINTOUT IS IN PROGRESS, PLEASE BE PATIENT" 100 FOR II=1 TO 1500: NEXT 110 DIM W(H,V), V(H,V) 120 Q=0: Z=0: X=RND(H) 130 FOR I=1 TO H 140 IF I=X THEN 160 150 LPRINT ":";: GOTO 170 160 LPRINT ": "; 170 NEXT I 180 LPRINT ":" 190 C=1: W(X,1)=C: C=C+1 200 R=X: S=1: GOTO 270 210 IF R<>H THEN 250 220 IF S<>V THEN 240 230 R=1: S=1: GOTO 260 240 R=1: S=S+1: GOTO 260 250 R=R+1 260 IF W(R,S)=0 THEN 210 270 IF R1=0 THEN 600 280 IF W(R1,S) <>0 THEN 600 290 IF S1=0 THEN 430 300 IF W(R,S1)<>0 THEN 430 310 IF R=H THEN 350 320 IF W(R+1,S)<>0 THEN 350 330 X=RND(3) 340 ON X GOTO 940,980,1020 350 IF S<>V THEN 380 360 IF Z=1 THEN 410 370 Q=1: GOTO 390 380 IF W(R,S+1)<>0 THEN 410 390 X=RND(3) 400 ON X GOTO 940,980,1090 410 X=RND(2) 420 ON X GOTO 940,980 430 IF R=H THEN 530 440 IF W(R+1,S)<>0 THEN 530 450 IF S<>V THEN 480 460 IF Z=1 THEN 510 470 Q=1: GOTO 490 480 IF W(R,S+1)<>0 THEN 510 490 X=RND(3) 500 ON X GOTO 940,1020,1090 510 X=RND(2) 520 ON X GOTO 940,1020 530 IF S<>V THEN 560 540 IF Z=1 THEN 590 550 Q=1: GOTO 570 560 IF W(R,S+1)<>0 THEN 590 570 X=INT(RND(0)*2+1) 580 ON X GOTO 940,1090 590 GOTO 940 600 IF S1=0 THEN 790 610 IF W(R,S1)<>0 THEN 790 620 IF R=H THEN 720 630 IF W(R+1,S)<>0 THEN 720 640 IF S<>V THEN 670 650 IF Z=1 THEN 700 660 Q=1: GOTO 680 670 IF W(R,S+1)<>0 THEN 700 680 X=RND(3) 690 ON X GOTO 980,1020,1090 700 X=RND(2) 710 ON X GOTO 980,1020 720 IF S<>V THEN 750 730 IF Z=1 THEN 780 740 Q=1: GOTO 760 750 IF W(R,S+1)<>0 THEN 780 760 X=RND(2) 770 ON X GOTO 980,1090 780 GOTO 980 790 IF R=H THEN 880 800 IF W(R+1,S)<>0 THEN 880 810 IF S<>V THEN 840 820 IF Z=1 THEN 870 830 Q=1: GOTO 990 840 IF W(R,S+1)<>0 THEN 870 850 X=RND(2) 860 ON X GOTO 1020,1090 870 GOTO 1020 880 IF S<>V THEN 910 890 IF Z=1 THEN 930 900 Q=1: GOTO 920 910 IF W(R,S+1)<>0 THEN 930 920 GOTO 1090 930 GOTO 1190 940 W(R1,S)=C 950 C=C+1: V(R1,S)=2: R=R1 960 IF C=H*V+1 THEN 1200 970 Q=0: GOTO 270 980 W(R,S1)=C 990 C=C+1 1000 V(R,S1)=1: S=S1: IF C=H*V+1 THEN 1200 1010 Q=0: GOTO 270 1020 W(R+1,S)=C 1030 C=C+1: IF V(R,S)=0 THEN 1050 1040 V(R,S)=3: GOTO 1060 1050 V(R,S)=2 1060 R=R+1 1070 IF C=H*V+1 THEN 1200 1080 GOTO 600 1090 IF Q=1 THEN 1150 1100 W(R,S+1)=C: C=C+1:IF V(R,S)=0 THEN 1120 1110 V(R,S)=3: GOTO 1130 1120 V(R,S)=1 1130 S=S+1: IF C=V*H+1 THEN 1200 1140 GOTO 270 1150 Z=1 1160 IF V(R,S)=0 THEN 1180 1170 V(R,S)=3: Q=0: GOTO 1190 1180 V(R,S)=1: Q=0: R=1: S=1: GOTO 260 1190 GOTO 210 1200 FOR J=1 TO V 1210 LPRINT "I"; 1220 FOR I=1 TO H 1230 IF V(I,J)<2 THEN 1260 1240 LPRINT " "; 1250 GOTO 1270 1260 LPRINT " I"; 1270 NEXT I 1280 LPRINT " " 1290 FOR I=1 TO H 1300 IF V(I,J)=0 THEN 1340 1310 IF V(I,J)=2 THEN 1340 1320 LPRINT ": "; 1330 GOTO 1350 1340 LPRINT ":"; 1350 NEXT I 1360 LPRINT ":" 1370 NEXT J 1380 END 