Breakdown of Einhver er að koma inn!
vera
to be
koma
to come
að
to (infinitive marker)
inn
in (motion inwards)
Questions & Answers about Einhver er að koma inn!
Why is einhver in the nominative case here?
In this sentence, einhver is the subject, meaning it is the person performing the action of coming in. Because it is the main subject of the sentence, it takes the nominative case.
Since einhver changes by gender, which gender is used for an unknown "someone"?
We use the masculine singular form (einhver) as the default when we don't know the gender of the person, or when referring to a general "someone".
What is the purpose of að in er að koma?
It creates the continuous tense, which is very similar to the "-ing" ending in English. You use the verb vera (to be) + að + the infinitive of the main verb (koma) to show that an action is happening right now.
Why does this sentence use inn instead of inni?
In Icelandic, words for "in" change depending on whether there is movement. Because the person is moving from the outside to the inside, we use the directional form inn. If they were already resting or standing inside, we would use the stationary location word inni.