isdef — checks variable existence
isdef(name [,where])
isdef(name)
returns %T
if the
variable namedname
exists and %F
otherwise.
Caveats: a function which uses isdef
may return a
result which depends on the environment!
isdef(name,'local')
returns %T
if the variable namedname
exists in the local
environment of the current function and %F
otherwise.
isdef(name,'nolocal')
returns
%T
if the variable named name
exists
in the full calling environment (including the global level) of the
current function and %F
otherwise.