[Avodah] Hebrew grammar - anticipatory noun

[Michael Makovi]

>  1- Geirim too were at Har Sinai, so in a sense geirim were born Jews
>  who just took a while to realize the fact. This is why the idiom is a
>  "ger shenisgayeir" -- the person was always omeid lihyos geir, even
>  before the geirus.

I'm not sure, but I suspect that perhaps it is a Hebrew idiom to name
a noun anticipatorily for its verb. For example, hanofel falling
without the parapet (with the exception of Rabbi Yishmael) - the
person who is going to fall is called the faller. Perhaps similarly,
we call a gentile who is going to convert, the convert who converts?

Any grammar curmudgeons know about this?

Mikha'el Makovi