List of static semantic checks

Thanks Alex for sifting through the Cool manual and making a list of all the static semantic checks that the "type checker" is supposed to check.  (The scare quotes are because, strictly speaking, a lot of these are not type rules, so really this is a static semantic analyzer which includes type checking and other checks).

1. [No undefined classes, pg. 7] If class C inherits B, then B must be
defined somewhere. This goes for any type specified by the programmer (ex:
let x:Foo := new Foo in 5, where Foo is never defined).

2. [No cycles in the class hierarchy, pg. 7] Class C must not inherit C,
nor should it inherit any other class that eventually inherits C.

3. [No class redefinitions, pg. 5] No two class definitions should use the
same name, i.e. "class C { ... }; ... class C { ... };" is invalid.

4. [No stdlib redefinitions, pg. 18] No class definition may use the names
Object, IO, Int, String, or Bool.

5. [Limited stdlib inheritance, pg. 18] No classes may inherit from Int,
Bool, or String. Classes may inherit from Object and IO.

6. [No attribute/method redefinitions, pg. 5] In the same class, no two
attributes/methods can have the same identifier. A method and an attribute
may share the same name, but not two methods or two attributes.

7. [No inherited attribute redefinitions, pg. 7] If class C inherits B,
and B defines an attribute "foo:Int", C must not contain an attribute
called foo.

8. [Limited inherited method redefinitions, pg. 10] If class C inherits B,
and B defins a method "foo(a:Int, b:Int):Int {}", then C can only
change the , it must not redefine the type signature of foo.

9. [No "self" redefinitions, pg. 12] It is an error to assign a value to
self, bind self in a let or case expression, or use self as the name of a
parameter to a method.

10. [Need a Main class / main method, pg. 19] Every program must have a
class called Main. In Main, there must be a method called main with no
parameters.

11. [All attributes/methods must typecheck, pg. 9] All methods and
attributes must pass the typechecker.