Definition: closure

Source: WordNet (r) 1.7

closure
     n 1: approaching a particular destination; a coming closer; a
          narrowing of a gap; "the ship's rapid rate of closing
          gave them little time to avoid a collision" [syn: closing]
     2: a rule for ending debate in a deliberative body [syn: cloture,
         gag rule]
     3: an obstruction in a pipe or tube; "we had to call a plumber
        to clear out the blockage in the drainpipe" [syn: blockage,
         block, occlusion, stop, stoppage]
     4: the act of blocking [syn: blockage, occlusion]
     5: termination of operations [syn: closedown, closing, shutdown]
     v : terminate debate by calling for a vote; "debate was
         closured"; "cloture the discussion" [syn: cloture]

Source: Webster's Revised Unabridged Dictionary (1913)

Closure \Clo"sure\ (?, 135), n. [Of. closure, L. clausura, fr.
   clauedere to shut. See Close, v. t.]
   1. The act of shutting; a closing; as, the closure of a
      chink.

   2. That which closes or shuts; that by which separate parts
      are fastened or closed.

            Without a seal, wafer, or any closure whatever.
                                                  --Pope.

   3. That which incloses or confines; an inclosure.

            O thou bloody prison . . . Within the guilty closure
            of thy walls Richard the Second here was hacked to
            death.                                --Shak.

   4. A conclusion; an end. [Obs.] --Shak.

   5. (Parliamentary Practice) A method of putting an end to
      debate and securing an immediate vote upon a measure
      before a legislative body. It is similar in effect to the
      previous question. It was first introduced into the
      British House of Commons in 1882. The French word
      cl[^o]ture was originally applied to this proceeding.

Source: The Free On-line Dictionary of Computing (2003-OCT-10)

closure

   1. <programming> In a reduction system, a closure is a data
   structure that holds an expression and an environment of
   variable bindings in which that expression is to be evaluated.
   The variables may be local or global.  Closures are used to
   represent unevaluated expressions when implementing
   functional programming languages with lazy evaluation.  In
   a real implementation, both expression and environment are
   represented by pointers.

   A suspension is a closure which includes a flag to say
   whether or not it has been evaluated.  The term "thunk" has
   come to be synonymous with "closure" but originated outside
   functional programming.

   2.  In domain theory, given a partially ordered
   set, D and a subset, X of D, the upward closure of X in D is
   the union over all x in X of the sets of all d in D such that
   x <= d.  Thus the upward closure of X in D contains the
   elements of X and any greater element of D.  A set is "upward
   closed" if it is the same as its upward closure, i.e. any d
   greater than an element is also an element.  The downward
   closure (or "left closure") is similar but with d <= x.  A
   downward closed set is one for which any d less than an
   element is also an element.

   ("<=" is written in LaTeX as \subseteq and the upward
   closure of X in D is written \uparrow_\D X).

   (1994-12-16)