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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".