is/are to infinitive
1) The construction is/are to + infinitive is used to talk about something that is due to happen in the future (i.e. expected, planned, required, supposed, or destined to).1 It can also be used in commands.
We were to complete the project by July — Debíamos completar el proyecto para julio
They weren't to return until three years had passed — No debían regresar hasta que hubieran pasado tres años
You are not to smoke in here! — ¡No debes fumar aquí!
Many bad things were to come from that decision — A raíz de esa decisión, pasarían muchas cosas malas
That young entrepreneur was later to become a rich man — Aquel joven emprendedor más adelante se convertiría en un hombre rico
2) A similar construction is is/are to be+ participle. This is passive.
The project is to be completed by July—El proyecto ha de completarse para julio
The prisoners were to be executed, but they were saved at the last minute—Los prisioneros debían ser ejecutados, pero se salvaron en el último momento
3) Is/are to be can also be followed by an adjective or noun, or it can be used with there is/are.
The weather is to be nice this week — Se prevé que haga buen tiempo esta semana
It turns out that her work is to be less of a burden — Resulta que su trabajo va a suponer menos carga de trabajo
There is to be an enquiry into the cause of the accident — Ha de haber una investigación sobre la causa del accidente
4) The to be + infinitive construction can also be used in a conditional clause with two different interpretations:
a) to express a precondition; in other words, this thing must happen first in order for the result of the condition to happen.
b) to express a hypothetical or unlikely condition; the subjunctive is the favoured option, and it can also be inverted (formal).
a) If you are (going) to succeed, you will need to work more — Si quieres tener éxito, tendrás que trabajar más
If change is (going) to happen, we will need to work together — Para que se dé un cambio, tendremos que trabajar juntos
He knew that if he was to succeed, he would have to work more (He would have to work more in order to succeed) — Sabía que si quería tener éxito, tendría que trabajar más (para lograrlo)
b) He knew if he were to succeed, he would have to work more (If he succeeded, he would then have to work more as a result) — Sabía que en el caso de que tuviera éxito, tendría que trabajar más (como resultado)
If the ice was/were to melt (if the ice melted), the sea level would rise — En el caso de que se derritiera el hielo, el nivel del mar subiría
Were the ice to melt, the sea level would rise — En el caso de que se derritiera el hielo, el nivel del mar subiría