thunk

thunk
    n 1: a dull hollow sound; "the basketball made a thunk as it hit
         the rim"
    

thunk
 /thuhnk/, n.

   1. [obs.]"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 which computes the
   expression and leaves 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. Microsoft and IBM have both defined, in their Intel-based systems,
   a "16-bit environment" (with bletcherous segment registers and 64K
   address limits) and a "32-bit environment" (with flat addressing and
   semi-real memory management). The two environments can both be running
   on the same computer and OS (thanks to what is called, in the
   Microsoft world, WOW which stands for Windows On Windows). MS and IBM
   have both decided that the process of getting from 16- to 32-bit and
   vice versa is called a "thunk"; for Windows 95, there is even a tool
   THUNK.EXE called a "thunk compiler".

   5. A person or activity 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 suggests 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".
    

thunk

   <programming> /thuhnk/ 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 which computes the
   expression and leaves the address of the result in some
   standard location.

   2. The term was later generalised to mean an expression,
   frozen together with its {environment} (variable values), for
   later evaluation if and when needed (similar to 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}.

   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
   suggests 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 realised (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".

   4. ({Microsoft Windows} programming) {universal thunk},
   {generic thunk}, {flat thunk}.

   [{Jargon File}]

   (1997-10-11)