function f/0
  function g/0
  end function
end function

# (function (@ 1 0-8) ‘f/0’
#   (.inner
#     (function (@ 2 2-10) ‘g/0’
#       (.inner nil)
#     )
#   )
# )
# :2:2–10: error: nested function definition
#    function g/0
#    ^^^^^^^^
# :1:0–8: note: outer function defined here
#  function f/0
#  ^^^^^^^^