[R] matrix position to list of coordinates

[Ana]

How can I extract a list of the positions in the matrix?
> A=matrix(1:8, nrow=2,ncol=4)
> A
     [,1] [,2] [,3] [,4]
[1,]    1    3    5    7
[2,]    2    4    6    8


Something like this

pos.A

1 1
1 2
1 3
1 4
2 1
2 2
2 3
2 4