When learning French, I was taught that an infinitive form, e.g. jouer, meant “to play” (or whatever). That is, the English translation of the verb was preceded by to.
The word à also means “to.” But there is an expression, cartes à jouer, for playing cards (literally “cards to play”) that puts an à before the infinitive verb. (And there are probably many similar expressions.) That would seem to have the word to twice, once for à, and once for the infinitive. And the expression would be translated, “cards, to to play.” At least that's the way it would look to an English speaker.
So when (and why) would French use à before a verb in the above context? Would it be redundant, or does à perform a function in this construction?