I'm trying to get the following behavior with AutoHotKey: When the A key is pressed, AHK holds down the S key until the D key is pressed. The following script isn't working as expected:

a::
    Send {s Down}
    return

d::
    if (GetKeyState("s", "P"))
        {
        Send {s Up}
        }
    return

Neither is the following:

a::
    release_s = 0
    Loop
        {
        SendInput, s
        if release_s
            break
        }
    return

d::
    release_s = 1
    return