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".
