# NOT RUN {
# ways to succeed:
is_freq(2) # => TRUE, but does NOT return the frequency 2.
is_freq(0:3) # => TRUE (for vector)
## ways to fail:
# is_freq(-1) # => FALSE + warning (negative values)
# is_freq(1:-1) # => FALSE (for vector) + warning (negative values)
# is_freq(c(1, 1.5, 2)) # => FALSE (for vector) + warning (non-integer values)
## note:
# is.integer(2) # => FALSE!
# }
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