BE + TO-infinitive

Be + to-infinitive is used to express:

• official arrangements:
  

  The Prime Minister is to visit India next month.

• official orders:
  

  At the end of the course, all students are to take a written exam.

• things that should be done:
  

  What am I to do?

• a possible aim when saying what should be done to reach it:
  

  If you are to work here for more than three months, you must have a residence permit.

• prohibition (only in the negative):
  

  You are not to do that again.

Be + to-infinitive can also be used in the past:

Mr Jones was to speak at the meeting. (it was arranged and he did)

But was/were + to + perfect infinitive means that the arranged event did not actually happen:

Mr Jones was to have spoken at the meeting, but he had to cancel because of his illness.