Lurk Beta

[porcuquine]

UPDATE: The items here (and others) will be worked on during Lurk Beta and are not blockers for reaching Beta.

This is a tracking issue for explicit languages modifying the behavior of the core Lurk language (i.e. the definition of the reduce step function) from that defined by Lurk Alpha.

• First-class Booleans Proposal: make nil and t first-class booleans. #570
• same-type? Support type predicates #658
• Add black-box so open need not be considered side-effecting for security. #848