The game code itself: 
 @g=map{$_=sprintf"%04o",$_;$_=~y@0-7@A-H@;$_}0..4095;for($|=1;@g>1;){
+print$f=$g
[@g*rand],$";($S=<>)=~/^[0-4]{2}$/?(@g=grep{$d=4-($a=($f^($e=$_))=~y@\
+0@@);$d-=
($c=index$e,$_)<0||(substr($e,$c,1)="")for(split'',$f);$&eq$a.$d}@g):p
+rint"\7"}

[download]
How to play it:
  1. Think of a string [A-H]{4}
  2. Start: perl game.pl
  3. The computer prints a guess [A-H]{4}
  4. You evaluate its guess by two digits (and <Enter>). The first digit is the number of common letters in good positions, and the 2nd digit is the number of common letters in wrong position. For example, the guess FFGA has value 21 if the string is DFGF.
  5. If the value wasn't 40, go back to step 3.
Enjoy! (But the computer always wins.)

In reply to a 240-byte game for you by Anonymous Monk

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