.SETFIRST list value

Changes the first member of list to be value.

The list input must be list and cannot be empty.

WARNING: Primitives whose names start with a period are dangerous. Their use by non-experts is not recommended. The use of .SETFIRST can lead to circular list structures, which causes infinite loops for some primitives; unexpected changes to other data structures that share storage with the list being modified; and the permanent loss of memory if a circular structure is released.

MAKE "mylist [1 2 3]
.SETFIRST :mylist 0
SHOW :mylist
[0 2 3]