Lookup and set Just 'x' Nothing Nothing Just () repeat with Labelable Just 'x' Nothing Nothing Just () Setting the missing tag does nothing: V{left='x'} Lenses compose: Just "leftleft" Lenses+prisms compose: Just 'x' Nothing Nothing "extension" Internal Structure: Record{v=V{left='x'} ,v2=V{left=()} ,v2'=V{left=()} ,v3=V{left='x'} ,v4=V{left=V{left="leftleft"} } ,v5=V{down="hi"} ,v6=V{down="hi"} ,v7=V{left='x'} }