Are there any languages in which alternation between corresponding nasal and non-nasal vowels is used solely for grammatical purposes?
When I speak of two vowels that "correspond" in this context, I mean two vowels that differ only by the feature plus or minus nasal.
Also, the alternation I am referring to would obtain across most or all the vowels in the language, such that, to use a nonce example...
a) /mezi, dize, noza, tezo, domu/ would all be in one tense, number, etc., and
b) /mezĩ, dizẽ, nozã, tezõ, domũ/ would all be in another tense, number, etc.