{FnDef {FnName ADDTOVAR}
{FnArgs VAR X{SUB 1} X{SUB 2} {ellipsis} X{SUB N}}
{Type NOSPREAD NLAMBDA}
{Text
Each {arg X{sub i}} that is not a member of the value of {arg VAR} is added to it, i.e. after {fn ADDTOVAR} completes, the value of {arg VAR} will be {lisp (UNION (LIST {arg X{sub 1}} {arg X{sub 2}} {ellipsis} {arg X{sub N}}) {arg VAR})}.  {fn ADDTOVAR} is used by {fn PRETTYDEF} for implementing the {lisp ADDVARS} command.  It performs some file package (see {SectionRef L!FilePackage}) related operations, i.e. "notices" that {arg VAR} has been changed.  Returns the atom {arg VAR} (not the value of {arg VAR}).

{Note which of ADDTOVAR's args are evaluated? ---mjs}
}}