The list concatenation operation has this representation in virtual code.
cat
]] = ((nil,nil),(nil,nil))
This function takes a pair of lists as an argument, an returns the list obtained by appending the right one to the left. The semantics of concatenation is what one would expect.
cat
]] (nil,
z)
= z
cat
]] ((
x,
y),
z)
= (
x,
[[cat
]] (
y,z))