adderall.dsl: Implement eqᵒ

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.internal: Add support for reifying cons values

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.internal: Do not re-reify already reified unbound vars

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.dsl: Implement pairᵒ

This needed another tweak to unify, to support cons-cons pair
unification too.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.dsl: Add an alias for eqᵒ

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderal.internal: Fix cons unification

When trying to unify a cons to an empty list, don't die horribly.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
tests: New tests from The Reasoned Schemer

This concludes chapter 2.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>