What do the functions tagged with @guidance desugar to?

[ahelwer]

I'm having difficulty understanding what the @guidance function tags do. As I understand it you generally have the flow:

lm = (some model)
@guidance(stateless=False)
def op(lm):
  lm += 'some text to generate'
  return lm
lm += op()

What does this actually translate to under the hood? How can I return multiple values from a function to capture information about the text that was generated for use by the caller?