Why isn't there an article after “comme” in this sentence?

Question

Regarde le cahier que Than reçoit comme cadeau de sa copine.

I was wondering why there isn't an 'un' before the 'cadeau'.

Answer 1

In French, it is very common for predicatives (attribut) to lack articles (Grevisse §586 b), and indeed in this construction, called an attribut du complément d'objet, "cadeau" is a predicative to "cahier", which is why the article drops.

Answer 2

I'm not sure Circeus answer (while valid) is enough to answer your question. These two sentences are correct:

Regarde le cahier que Than reçoit comme cadeau.
Regarde le cahier que Than reçoit comme un cadeau.

In the first one, the speaker adds the precision that he/she talks about the notebook which was offered as a gift. In the second sentence, Than receives a notebook and a precision is added that it looks like a gift, but maybe it isn't.

Note: With this simple construction, because the article disappears, French is not able to make the difference beetween “as a gift” and the less common “as the gift”. One would need complex paraphrases to express the latest.