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As a starting point I'll write up what I found about these functions before. I'm hoping someone will take a better look at them and will write a more complete answer.

Spelunking in version 8,

Internal`AddPeriodical[Print["boo!"], 3]

Now you get a boo! every 3 seconds.

Internal`Periodicals[]

(* ==> {Print["boo!"]} *)

Now do

Internal`RemovePeriodical[Print["boo!"]]

to stop it.

Internal`Periodicals[]

(* ==> {} *)

Note that AddPeriodical and RemovePeriodical have HoldFirst.

Internal`$ThisPeriodical seems to be undefined during normal evaluations, while it is set to the currently executing periodical (wrapped in HoldForm) when a periodical is being executed.

Most (all?) of the version 8 functionality seems to be implementable in terms of these.

As a starting point I'll write up what I found about these functions before. I'm hoping someone will take a better look at them and will write a more complete answer.

Spelunking in version 8,

Internal`AddPeriodical[Print["boo!"], 3]

Now you get a boo! every 3 seconds.

Internal`Periodicals[]

(* ==> {Print["boo!"]} *)

Now do

Internal`RemovePeriodical[Print["boo!"]]

to stop it.

Internal`Periodicals[]

(* ==> {} *)

Note that AddPeriodical and RemovePeriodical have HoldFirst.

Internal`$ThisPeriodical seems to be undefined during normal evaluations, while it is set to the currently executing periodical (wrapped in HoldForm) when a periodical is being executed.

Most (all?) of the version 8 functionality seems to be implementable in terms of these, provided that they work the same way in version 7 as in 8 (which I cannot test).

As a starting point I'll write up what I found about these functions before. I'm hoping someone will take a better look at them and will write a more complete answer.

Spelunking in version 8,

Internal`AddPeriodical[Print["boo!"], 3]

Now you get a boo! every 3 seconds.

Internal`Periodicals[]

(* ==> Print["boo!"] *)

Now do

Internal`RemovePeriodical[Print["boo!"]]

to stop it.

Internal`Periodicals[]

(* ==> {} *)

Note that AddPeriodical and RemovePeriodical have HoldFirst.

I don't know what Internal`$ThisPeriodical is, but I suspect it might have a special value during the execution of a periodical (no time to spelunk more, sorry!)

As a starting point I'll write up what I found about these functions before. I'm hoping someone will take a better look at them and will write a more complete answer.

Spelunking in version 8,

Internal`AddPeriodical[Print["boo!"], 3]

Now you get a boo! every 3 seconds.

Internal`Periodicals[]

(* ==> {Print["boo!"]} *)

Now do

Internal`RemovePeriodical[Print["boo!"]]

to stop it.

Internal`Periodicals[]

(* ==> {} *)

Note that AddPeriodical and RemovePeriodical have HoldFirst.

Internal`$ThisPeriodical seems to be undefined during normal evaluations, while it is set to the currently executing periodical (wrapped in HoldForm) when a periodical is being executed.

Most (all?) of the version 8 functionality seems to be implementable in terms of these.

Spelunking in version 8,

Internal`AddPeriodical[Print["boo!"], 3]

Now you get a boo! every 3 seconds.

Internal`Periodicals[]

(* ==> Print["boo!"] *)

Now do

Internal`RemovePeriodical[Print["boo!"]]

to stop it.

Internal`Periodicals[]

(* ==> {} *)

Note that AddPeriodical and RemovePeriodical have HoldFirst.

I don't know what Internal`$ThisPeriodical is, but I suspect it might have a special value during the execution of a periodical (no time to spelunk more, sorry!)

As a starting point I'll write up what I found about these functions before. I'm hoping someone will take a better look at them and will write a more complete answer.

Spelunking in version 8,

Internal`AddPeriodical[Print["boo!"], 3]

Now you get a boo! every 3 seconds.

Internal`Periodicals[]

(* ==> Print["boo!"] *)

Now do

Internal`RemovePeriodical[Print["boo!"]]

to stop it.

Internal`Periodicals[]

(* ==> {} *)

Note that AddPeriodical and RemovePeriodical have HoldFirst.

I don't know what Internal`$ThisPeriodical is, but I suspect it might have a special value during the execution of a periodical (no time to spelunk more, sorry!)