Data Structure Primitives
_setFirst list value
command. Changes the first member of "list" to be "value". WARNING: Primitives whose names start with a underbar are DANGEROUS. Their use by non-experts is not recommended. The use of _setFirst can lead to circular list structures, which will get some Logo primitives into infinite loops; unexpected changes to other data structures that share storage with the list being modified; and the loss of memory if a circular structure is released.