My friends and I very seldom, if ever, use "yeah". Instead, we say "yah", rather like the German "ja". I have no idea where that comes from, since German influence in Singapore is practically non-existant. But there you go.
However, if a question is asked in a more formal setting, we naturally go back to "yes". Or say somebody of a higher authority asks you a question (eg a teacher asking a student something), you answer "yes". It's more formal, and shows more respect than "yah".
But that's an interesting question. I had to think about it before giving an answer. :p
metwin1
