type-index := (: BTreeIsEOF BTreeIs<AST,Type>);

typeof := λ(: t AST). (: (
   (.lookup( type-index t TAny ))
) Type);

ascript := λ(: t AST)(: tt Type). (: (
   (.bind( (as (& type-index) BTreeIs<AST,Type>[]) t tt ))
) Nil);