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".
[glossary]