[R] nls and start values evaluation

[Petr PIKAL]

Dear all

I have troubles with correct evaluating/structure of nls input

x<-1:10
y<-1/(.5-x)+rnorm(10)/100

form <- structure(list(a = list(quote(y ~ 1/(a - x)), "list(a=mean(y))")), 
 .Names = "a")

This gives me an error due to not suitable default starting value
fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y))

This works and gives me a result
fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y), start=list(a=mean(y)))

How to organise list "form" and call to nls to enable to use other then 
default starting values.
I thought about something like

fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y), start=get(form [[1]] 
[[2]]))
but this gives me an error so it is bad function. (BTW I tried eval, 
assign, sustitute, evalq and maybe some other options but did not get it 
right.

I know I can put starting values interactively but what if I want them 
computed by some easy way which is specified by second part of a list, 
like in above example.

If it matters
WXP,  R2.9.0 devel.

Regards
Petr