LocalJumpError

proc.rb

def inner_proc
  _proc = Proc.new {return 42}
  puts _proc.call
end

def outter_proc(_proc)
  puts _proc.call
end

inner_proc # => 42

proc = Proc.new {return 42}
outter_proc(proc) # => LocalJumpError: unexpected return

The context outter_proc was calling can not return, the same as defining proc into a method, method has return, but you cant return from an exited method.