Add instructions that the TA can follow to grade your project.

. VISUAL CHANGES

• rad intro screen woo. adding some plot/ motivation.
• added boundaries
  • purely ascetic and because the lack thereof annoyed me
  • space invaders don't cross boundaries
• changed minimum screen size
• some random ascetic tweaks all around i can't remember . FUNCTIONALITY CHANGES
• encroachers can "return fire" semi-randomly
  • not really randomly, because trying to create pseudo-random behavior with, like, the mod function alone was doomed to failure.
  • at least it looks plausible!
• the player has three lives.
  • countdown displayed in upper left corner
  • once player is hit by return fire three times, the game is over
• game over screen with option to replay or exit

Syntactic sugar to eliminate common if? + cast idiom in OAT. Use castnull!

if? (Object o = item.obj) {
  cast (Foo f = o) {
    f.print();
  } else print_string("failed cast");
} else print_string("failed null");

becomes

castnull (Foo f = item.obj) {
  f.print();
} else print_string("failed null/cast");

Or, in encroach.oat:

if?( Object o = item.obj ) {
  cast (DelayedObject dobj = o) {
    dobj.draw();
  }
}

becomes

castnull ( DelayedObject dobj = item.obj ) {
  dobj.draw();
}

This is essentially a modification to the parser that unrolls a castnull into an if? dereference followed by a cast from Object. This makese the pseudo-polymorphism used in a datatype like List work a bit better/cleaner.

To see that the syntax doesn't change the program semantics, compile tests/encroach.oat and tests/encroach_orig.oat, diff them, and see that the same LL code is generated for both.