determines which forms ld evaluates

ld-missing-input-ok is an ld special (see ld). The accessor is (ld-missing-input-ok state) and the updater is (set-ld-missing-input-ok val state). ld-missing-input-ok must be either nil, t, or :warn. The initial value of ld-missing-input-ok is nil.

The general-purpose ACL2 read-eval-print loop, ld, is controlled by various flags that control its behavior, and ld-missing-input-ok is one of them. In brief, the first argument of ld can indicate a file from which to read input. If the file does not exist, it is an error by default, but ld becomes essentially a no-op if t or :warn is supplied for :ld-missing-input-ok, where :warn prints a warning. Also see ld.