o42a-0.2.1 Release Notes

This release introduces a macro support.

The macro is an object, which value is an arbitrary expression. This expression can be substituted to the program with a macro expansion unary operator:

#Expression resolved to a macro

The macro field can be declared as any other one, but a shorter syntax is also supported:

#Macro field := expression

When a macro field is overridden, it is re-expanded in the derived object thus rewriting the dependent definitions. This can be used to create generics for example:

Generic :=> void (
  #Type :=< void // Type parameter 
  Link :=< (`#type) void
Integer generic := generic (
  Type = integer // Override the type parameter
  Link = 123     // Integer will be substituted as a new link interface.

As for now, the macro expansion can only be used as a type parameter. But this limitation will be removed over time to support the macro expansion in (almost?) all places, where arbitrary expressions can be used.