[newbie] return index(s) for value?

Is there a function 'foo' such that, given an array and a value,
iff the value is present in the array, it returns the index(s) of
the value? E.g.,

matrix(1:9, nrow=3) -> grid
grid

     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9

foo(grid, median(grid))

[1] c(2,2)

just use the argument arr.ind of ?which:

which(grid == median(grid), arr.ind = TRUE)

Note that it defaults to FALSE.