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 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. 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
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".
