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Now, we bring it all together into a first generative program using the instruct-validate-repair pattern: 
import mellea
from mellea.stdlib.requirement import req, check, simple_validate
from mellea.stdlib.sampling import RejectionSamplingStrategy

def write_email(m: mellea.MelleaSession, name: str, notes: str) -> str:
    email_candidate = m.instruct(
        "Write an email to {{name}} using the notes following: {{notes}}.",
        requirements=[
            req("The email should have a salutation"),  # == r1
            req(
                "Use only lower-case letters",
                validation_fn=simple_validate(lambda x: x.lower() == x),
            ),  # == r2
            check("Do not mention purple elephants."),  # == r3
        ],
        strategy=RejectionSamplingStrategy(loop_budget=5),
        user_variables={"name": name, "notes": notes},
        return_sampling_results=True,
    )
    if email_candidate.success:
        return str(email_candidate.result)
    else:
        return email_candidate.sample_generations[0].value


m = mellea.start_session()
print(write_email(m, "Olivia",
                  "Olivia helped the lab over the last few weeks by organizing intern events, advertising the speaker series, and handling issues with snack delivery."))
The instruct() method is a convenience function that creates and then generates from an Instruction Component, req() similarly wraps the Requirement Component, etc. Chapter 2 will takes us one level deeper into understanding what happens under the hood when you call m.instruct().