Infix version of eqo/2.

      The Law of <~>
v <~> w  is the same as  w <~> v.

A macro for conj/2 — the logic and.

Example macro expanding :

ando do
  g1
  g2
  g3
end

# = expand to =>

conj(zzz(g1),
  conj(zzz(g2),
    zzz(g3)))

A macro for a list ando/1 in oro/1.

      The Law of conde
To get more values from conde ,
pretend that the successful conde
line has failed, refreshing all variables
that got an association from that line.

• conde is written conde and is pronounced “con-dee”.

• conde is the default control mechanism of Prolog. See William F. Clocksin. Clause and Effect. Springer, 1997.

Perform the unification.

A goal that fails.

A macro to create fresh logic variables.

      The Law of Fresh
If x is fresh, then  v <~> x  succeeds
and associates x with v.

Example macro expanding :

fresh [a, b, c] do
  g1
  g2
  g3
end

# = expand to =>

call_with_fresh fn a ->
  call_with_fresh fn b ->
    call_with_fresh fn c ->
      ando do
        g1
        g2
        g3
      end
    end
  end
end

A macro for disj/2 — the logic or.

Just like ando/1.

A goal that succeeds.

One-step walking

Walking until the value is not Var.t, which does not care about other vars in the result value.

Invers-η-delay

The act of performing an inverse-η on a goal and then wrapping its body in a lambda we refer to as inverse-η-delay.

Invers-η-delay is an operation that takes a goal and returns a goal, as the result of doing so on any goal g is a function from a state to a stream.