Ethan A Merritt wrote:
> On Monday 29 May 2006 04:06 am, Hans-Bernhard Br=F6ker wrote:
>=20
>>The problem is in 'reset': that command is not supposed to as much as=20
>>*look* at the user-defined variables in the first place, much less=20
>>remove any of them, whether they're in limbo or not.
>=20
>=20
> It only removes undefined variables. This is only garbage-collection
> mechanism we have for such space, so if you remove it we will end
> up with the opposite problem of a memory leak.
>=20
> The issue is that the parsing code uses add_udv(), which results in=20
> space allocation for every variable mentioned, whether or not it is
> a correctly defined variable. For example:
> print nonsense
> allocates space for a variable "nonsense" before reporting that it
> is undefined. This space will only be released if you later define
> "nonsense" properly, or do a reset.=20
>=20
>=20
>>gnuplot> f(x) =3D x+a
>>gnuplot> g(x) =3D x+b
>>gnuplot> plot f(x)
>> undefined variable: a
>=20
> I am inclined to say that the definition of f(x) should fail if there=20
> is no previously-defined variable 'a'.
Well, that is an alternative. It's the same thing as I was just looking =
at for checking that the number of input variables to a function match. =
(A very useful feature, BTW.) At first my thinking was that gnuplot shou=
ld complain if it tries to use a function that hasn't been defined and do=
esn't have the correct number of input variables.
But then I saw that gnuplot seems to be set up to not check/verify anythi=
ng until interpretation. I personally wouldn't get into a programming ha=
bit of using variables I haven't defined, but I can live with that philos=
ophy.
If that is the concept, then neither functions (as is currently the case)=
nor variables can be removed even if they are undefined, unless intentio=
nally removed.
Whatever the case, both functions and variables should behave the same wa=
y.
As for cleaning up the variable space, an eventual 'reset' or 'unset' to =
do that would be good.
I would say that having the function argument keep track of the memory po=
inter as well as the linked list of variables is marginal programming pra=
ctice. Pointers in lists are something that should only be used temporar=
ily on the fly, and not stored in multiple places. I see the issue, howe=
ver, which is speed. Can the pointers be looked up at the time of the pl=
ot command, used in the command, and then discarded? [Keep in mind I don=
't understand the code too well, that's why I punted.]
> Alternatively, the code that creates an evaluation stack for 'f(x)'
> could initialize a to 0 rather than leaving it undefined.
That I don't think is acceptable. If I define a function involving some =
variable I've not defined and gnuplot assumes it equals zero, that wouldn=
't be good. I could never know the difference in some instances of compl=
icated functions I'm not familiar with.
Dan
|
