<s5>Æliens</s5> -- slide(s)

Typing -- protection against errors

static -- type checking at compile time
strong -- all expressions are type consistent

Untyped -- flexibility

bitstrings, sets, $%l$ -calculus

Exceptions to monomorphic typing:

overloading, coercion, subranging, value-sharing (nil)

slide: The nature of types

Flavors of polymorphism

inclusion polymorphism -- to model subtypes and inheritance
parametric polymorphism -- uniformly on a range of types
intersection types -- coherent overloading

slide: Flavors of polymorphism

Inheritance -- incremental modification

Result = Parent + Modifier

Example: $R = { a1, a2 } + { a2, a3 } = { a1, a2, a3 }$

Independent attributes: M disjoint from P
Overlapping attributes: M overrules P

Dynamic binding

$R = {...,P_i: self ! A,...} + { ...,M_j: self ! B, ... }$

slide: Inheritance as incremental modification