file.groovy

/*
0 x..-1
1 0..x
*/

def test(index, myindex){

ary = [
    /*0*/ 7, /*1*/ 8, /*2*/ 9, 
    /*3*/ 17, /*4*/ 18, /*5*/ 19]

println "$index $myindex"

start = 0 + myindex * ( 1 - index);
end = -1 + ( ( myindex + 1 ) * index**2 );

println "$start $end"

ary[start..end]
}

[
    // starts
    [ [0, 0] /* 0 ..-1 */, [7,8,9,17,18,19] ],
    [ [0, 1] /* 1 ..-1 */, [  8,9,17,18,19] ],
    
    // ends
    [ [1, 3] /* 0 .. 3 */, [7,8,9,17      ] ],
    [ [1, 5] /* 0 .. 5 */, [7,8,9,17,18,19] ],
].each { args, expc ->
def act = test(args[0], args[1])
    assert(expc == act)
    println act
}

null