Basic ABC's

Singleton
- Nothing
- Undefined
- Done (EOF signal)
Callable
- Function/Closure
- Continuation
- BoundMethod
Iterable (for ... in ... loops)
- List
  - String
  - Bytevector
- Set
- Record
- Range
Iterator (for ... of ... loops)
Numeric
- Scalar
  - Float
  - Rational
  - Integer
- Complex < Vector
Symbol
- Keyword
CodeType
- Expression < List
- Block < List, String
- Comment < String
- Whitespace
- EOL
- Pattern < List
- PatternCombinator
  - Repeat
  - Alternate
  - Match
  - Lookahead/Lookbehind
  - etc.
Error < Continuation
- MathError
  - DivideByZeroError
- LookupError
  - IndexError
  - KeyError
    - AttributeError
  - NameError
- AssertionError
- IOError
  - EOFError
  - FileNotFoundError
  - FIleExistsError
  - ImportError
    - NoModuleError < FileNotFoundError
    - NoExportError < LookupError
  - OSError
- UserInterrupt
- RuntimeError
  - RecursionError
  - SyntaxError
    - IndentationError
  - SystemError
- OutOfMemoryError
- TypeError
Stream < Iterator
- BytesStream
- TextStream
- ...everything else