Options

In maybe.cecil:

abstract object maybe[`T];
extend type maybe[`T] subtypes maybe[`S >= T];
  signature if_some_none(maybe[`T], if_some:&(T):`T1, if_none:&():`T2):T1|T2;
  method if_some(m@:maybe[`T], if_some:&(T):void):void;
  method if_none(m@:maybe[`T], if_none:&():void):void;
  method is_some(m@:maybe[`T]):bool;
  method is_none(m@:maybe[`T]):bool;
  signature value(maybe[`T]):T;
  method value(m@:maybe[`T1], if_none:&():`T2):T1|T2;
template object some[`T] isa maybe[T];
extend type some[`T] subtypes some[`S >= T];
  field value(@:some[`T]):T;
  method if_some_none(s@:some[`T], if_some:&(T):`T1, if_none:&():`T2):T1|T2;
  method some(value:`T):some[T];
  method some[`T](value:T):some[T];
  method print_string(s@:some[`T]):string;
concrete object none[`T] isa maybe[T];
extend type none[`T] subtypes none[`S >= T];
  method if_some_none(@:none[`T], if_some:&(T):`T1, if_none:&():`T2):T1|T2;
  method value(@:none[`T]):T;
extend object maybe[`T <= comparable[T]] isa comparable[maybe[T]];
  method =(@:maybe[`T <= comparable[T]], @:maybe[`T]):bool;
  method =(s1@:some[`T <= comparable[T]], s2@:some[`T]):bool;
  method =(@:none[`T <= comparable[T]], @:none[`T]):bool;
extend object maybe[`T <= hashable[T]] isa hashable[maybe[T]];
  method hash(s@:some[`T <= hashable[T]], range:int):int;
  method hash(@:none[`T <= hashable[T]], range:int):int;

The maybe[T] parameterized type represents either a value of type T or no value, akin to ML's option datatype. maybes are useful where an explicit null pointer might be used in some other language, but the possibility for null is explicit when using maybes.