Scheme State

[Ralph Little]

Hi,
I'm doing some Scheme to parse music structures, but I'm finding that I need to
save and update some state information as I parse the tree.

I could set aside some globally scoped structure that is not passed around the
various calls while I'm parsing the tree but this feels wrong.

Could some Scheme guru out there point me in the right direction?

As a hint to what I'm up to, I'm parsing through bars of music and maintaining a
list of accidentals since the beginning of the bar so that I can implement the
"default" accidental style. 

Any help would be really appreciated!

Regards,
Ralph