Cycles don't print in REPL

[jcubic]

This creates stack overflow:

lips> '#0=(a b c . #0#)

even that this works

(display '#0=(a b c . #0#))
;; ==> #0=(a b c . #0#)
(write '#0=(a b c . #0#))
;; ==> #0=(a b c . #0#)

[jcubic]

the problem was that the quote macro was running resolve_promises before marking the data as a cycle.

[jcubic]

The better fix was to mark cycles on a parser level when a datum was used. This should not slow down the code.

[jcubic]

This fix also make this works (kind of):

lips> #0=(a b c . #0#)
Unbound variable `a'

There is a need for a function is_cycle() and the code should throw an error because the cycle is found in the code.