This works as soon as #732 is merged, since then maplist/N and foldl/N
are deterministic in the required cases.
This also resolves the extra choicepoint of time/1 (see #378).
Many thanks to @notoria for implementing better indexing in #732,
which allowed me to find this opportunity for improvement!
Without this, we do not get a (timely) prompt in cases like:
?- format("press a key: ", []), get_single_char(C).
whereas for example write/1 already works in such cases:
?- write('press a key: '), get_single_char(C).
press a key:
