@main[]
$sDir[182_dir]
^use[$sDir/a1.p]
^use[$sDir/a2.p]

^^a:a1[]: ^a:a1[]
^^a:a2[]: ^a:a2[]
^^a:a3[]: ^a:a3[]
^^b:b1[]: ^b:b1[]

<hr />

# override 'a' class and add 'c' class
^use[182_dir/a3.p]

^^a:a1[]: ^a:a1[]
^^a:a2[]: ^try-catch{^a:a2[]}
^^b:b1[]: ^b:b1[]
^^c:c1[]: ^c:c1[]
^^c:c2[]: ^try-catch{^c:c2[]}