[R] area between two curves, but one is not continuous

[Anton Meyer]

Hello,

I want to colorize the area between two curves, but one of these
curves isn't continuous.

The best solution I found is the 2nd example in the help of polygon,
but how can I get no area filling for the missing data in the 2nd curve.

example:

x1 = c(1:8)
x2 = c(1:8)
y1 = c(1,5,6,1,4,5,5,5)
y2 = c(0,3,3,NA,NA,1,3,4)

plot(x1,y1,type="l")
lines(x2,y2)

for the missing parts I want no filling.

so for this examples the code would be:
polygon(c(1:3,3:1),c(y1[1:3],rev(y2[1:3])),col="green")
polygon(c(6:8,8:6),c(y1[6:8],rev(y2[6:8])),col="green")

How can I generalize this for a longer curve with more data?

AxM