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.