Copy each element l[i] in l and insert count new copies of l[i] immediately after l[i] in l.
abjad> l = [1, 1, 2, 3, 5, 5, 6]
abjad> listtools.repeat_elements_to_count(l, 2)
[1, 1, 1, 1, 2, 2, 3, 3, 5, 5, 5, 5, 6, 6]
abjad> l = [1, -1, 2, -3, 5, -5, 6]
abjad> listtools.repeat_elements_to_count(l, 2)
[1, 1, -1, -1, 2, 2, -3, -3, 5, 5, -5, -5, 6, 6]
Raise TypeError when l is not a list:
abjad> listtools.repeat_elements_to_count('foo')
TypeError
Todo
Generalize count from a single integer count to a list of integer counts. Read values cyclically.