Talk:Thunk

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On the topic of LISP..

Not so, a thunk stored in a SASL list allows delayed evaluation of the thunk until the value is absolutely needed, a common example is a list of all prime numbers where the list of elements are represented with a thunk that is used to derive the prime numbers, filling in the contents with the primes as they are provided by the thunk, thus allowing repeated accesses of the same list elements takes constant time because they are already evaluated. The thunk requires access to the list indices (thunk implemented as a lambda function). .

Actually, a lambda function can be used to create a list of thunks, but the thunks are determined by the lambda function, so.. It's been a while since I've coded LISP, ever since I learned the language, great for learning but I wouldn't code in it.. Ask Suzanne Sluizer she knows..

--Rofthorax 09:56, 24 August 2005 (UTC)


No No No! Thunking is more general than that! Probably needs a reference to Algol implementations which used thunking... -- 81.79.64.46 11:14, 3 May 2004 (UTC)

For a good discussion, see:

http://compilers.iecc.com/comparch/article/98-03-043

The legend that I heard was that, generically, a "thunk" is a function (or procedure) which takes no arguments, and returns no values, and that it was coined by Donald Knuth in The Art of Computer Programming, who came up with thunk as an anagram of his surname, and as a way to describe a minimal function. I don't have my copy handy to verify. But this seems like a general definition which would apply to invoking the continuation of closures, which usually take much longer than a little thunk should.

According to the Internet's famous jargon file:

File: jargon.info

:thunk: /thuhnk/ n. 1. "A piece of coding which provides an
   address", according to P. Z. Ingerman, who invented thunks
   in 1961 as a way of binding actual parameters to their formal
   definitions in Algol-60 procedure calls.  If a procedure is called
   with an expression in the place of a formal parameter, the compiler
   generates a {thunk} to compute the expression and leave the
   address of the result in some standard location.  2. Later
   generalized into: an expression, frozen together with its
   environment, for later evaluation if and when needed (similar to
   what in techspeak is called a `closure').  The process of
   unfreezing these thunks is called `forcing'.  3. A
   {stubroutine}, in an overlay programming environment, that loads
   and jumps to the correct overlay.  Compare {trampoline}.
   4. People and activities scheduled in a thunklike manner.  "It
   occurred to me the other day that I am rather accurately modeled by
   a thunk --- I frequently need to be forced to completion." ---
   paraphrased from a {plan file}.

   Historical note: There are a couple of onomatopoeic myths
   circulating about the origin of this term.  The most common is that
   it is the sound made by data hitting the stack; another holds that
   the sound is that of the data hitting an accumulator.  Yet another
   holds that it is the sound of the expression being unfrozen at
   argument-evaluation time.  In fact, according to the inventors, it
   was coined after they realized (in the wee hours after hours of
   discussion) that the type of an argument in Algol-60 could be
   figured out in advance with a little compile-time thought,
   simplifying the evaluation machinery.  In other words, it had
   `already been thought of'; thus it was christened a `thunk',
   which is "the past tense of `think' at two in the morning".
I'd read this before too, which is why the "no known root" at the top of the article surprised me. Could someone paraphrase the "past tense of think" explanation in the article? I'm too tired to do it well right now. PeteVerdon 21:34, 2 January 2006 (UTC)
Is the Jargon File really reliable enough to be included in encyclopedic content? If there's an actual non-speculative source for the "past tense of think" explanation, that ought to be cited -- otherwise I don't think that the possible etymology of the word is really important enough to be included, since there are at least three distinct, unverified etymologies floating around. --bmills 20:25, 5 January 2006 (UTC)
who would have thunk it? --ZhuLien 2:14, 26 March 2007 (UTC)

[edit] Splittify me!

As far as my mind can tell (which is quite far, I believe), two meanings of the word "thunk" are used on this page. I feel that each should have a separate page... I dunno why, though :-) --Ihope127 03:42, 22 August 2005 (UTC)

I reckon all 3 meanings should be split. The non-computer term is the most commonly used one I'd guess as the computer terms would only be used by programmers. --ZhuLien 13:08, 23 July 2006 (GMT+10)

[edit] Flat thunk

I removed the following and replaced it with a shorter summary based on the first half:

A flat thunk consists of a pair of dlls (one 32bit and one 16bit) that are used to translate calls from 32bit code to 16bit code. To allow the two dlls to communicate, some intermediate code must be used to translate memory addresses (pointers) between platforms. If you have any past experience with 16bit process memory calls, you may recall that they consist of a pointer to a memory segment and the offset into that memory segment. This is different than a 32bit process memory pointer which consists of an absolute address to the memory being accessed. So, the problem, in a nutshell, is translating segment + offset pointers into absolute addresses. VB programmers don't usually need to worry about things like memory pointers, but the problem is that ALL software is ultimately based on memory pointers. It is the IDE and the programming language that hide these ugly details from us but when you get right down to it, every variable, function, sub and etc... that you write (in any language) consists of an address in memory. Now, imagine a 16bit dll being loaded into a 32bit process where none of the memory addresses match up on either side of the function calls. It just plain can't be done without proper translation. By Gaurav Bhaskar Microsft Support v-2gabha@mssupport.microsoft.com

Cammy 19:25, 29 December 2006 (UTC)

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