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.

