Halting problem simple proof in Ruby

halting_problem.rb

# Assume we are able to write a function, magical_solver, which can magically
# determine whether or not a function halts
def magical_solver(source_code)
  # outputs 'true' if fn.source_code halts
  # outputs 'false' if fn.source_code doesn't halt
end

def always_halt
  # Always halts
end

def never_halt
  # Never halts (goes into infinite loop)
end

def flipper(source_code)
  # If fn halts, output a program that doesn't halt
  # If fn doesn't halt, output a program that does halt
  if magical_solver(source_code)
    never_halt.source_code
  else
    always_halt.source_code
  end
end

magical_solver(flipper(always_halt.source_code)) # false
magical_solver(flipper(never_halt.source_code)) # true

# What if we pass flipper into itself?
magical_solver(flipper(flipper.source_code))

# Possibility A: flipper is a good program
# magical_solver will tell us that flipper is a bad program

# Possibility B: flipper is a bad program
# magical_solver will tell us that flipper is a good program

# Both possibility A and possibility B are contradictions, therefore magical_solver cannot exist,
# and we can never determine whether or not a program halts.