making objects and types in io

gistfile1.io

#differential inheritance
#making types (objects with a type field)
Shape := Object clone
Shape area := method(width * height)
Shape width := 5
Shape height := 9
Rect := Shape clone
Square := Shape clone
Ellipse := Shape clone

#making objects (without a type field, note the lowercase start
#to the variable name)
box := Rect clone 
boxyBox := Square clone 
egg := Ellipse clone

#
writeln("Differential inheritance")
box slotNames println         # => list()
boxyBox slotNames println     # => list()
egg slotNames println         # => list()

Rect slotNames println        # => list(type)
Square slotNames println      # => list(type)
Ellipse slotNames println     # => list(type)
Shape slotNames println       # => list(height, type, width, area)

#seems like hasSlot will crawl up the inheritance tree
box hasSlot("area") println # => true
Rect hasSlot("area") println # => true