I keep getting this error--- syntax: invalid iteration specification

Seems we ran into the problem of using significant whitespace so appending to r ended up inside the inner loop.

Here I have moved it outside.

function distance(x, y, a, b, coverage) 
    r = Float64[]
    for (i,xv) in enumerate(x)
        R = Float64[]
        for (j, jv) in enumerate(a)
            if coverage[j][i] == 1
                push!(R, ((x[i]-a[j])^2 + (y[i]-b[j])^2)^0.5)
            end
         end
         if length(R) > 0
             push!(r, maximum(R))
         end
    end
    return r
end