double a-prefixing?

[Beverly Flanigan]

At 01:28 PM 6/25/2004 -0400, you wrote:
>Another random a-prefixing wierdness... last Saturday, my mother-in-law-to-be
>said:
>"I musta been a-gonna write on it." (describing some odd scrap of paper she
>found).
>
>It struck me (and my husband-to-be) as odd.  Now, forgive the bad syntactic
>description, but I think this is the first time I've heard the a-prefix on the
>"future going" rather than the "movement going".
>
>-dsb
>Douglas S. Bigham
>Department of Linguistics
>University of Texas - Austin
>http://hometown.aol.com/capn002/myhomepage/index.html

It's not really so weird, and it's not quite future.  If you "formalize"
it, it's "I must have been going to write on it" = planning to, therefore
present perfect progressive?  But even if it's future gonna, think of "I'm
a-gonna do it"--not weird at all.