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Old English hoc "hook, angle," perhaps related to Old English haca "bolt," from Proto-Germanic *hokaz/*hakan- (cf. Old Frisian hok, Middle Dutch hoek, Dutch haak, German Haken "hook"), from PIE *keg- "hook, tooth" (cf. Russian kogot "claw"). For spelling, see hood (n.1).
Boxing sense of "short, swinging blow with the elbow bent" is from 1898. Figurative sense was in Middle English (see hooker). By hook or by crook (late 14c.) probably alludes to tools of professional thieves. Hook, line, and sinker "completely" is 1838, a metaphor from angling.
? Object Oriented Kernel. Delphia. An object-oriented extension of Delphia Prolog.
A software or hardware feature included in order to simplify later additions or changes by a user.
For example, a simple program that prints numbers might always print them in base 10, but a more flexible version would let a variable determine what base to use; setting the variable to 5 would make the program print numbers in base 5. The variable is a simple hook. An even more flexible program might examine the variable and treat a value of 16 or less as the base to use, but treat any other number as the address of a user-supplied routine for printing a number. This is a hairy but powerful hook; one can then write a routine to print numbers as Roman numerals, say, or as Hebrew characters, and plug it into the program through the hook.
Often the difference between a good program and a superb one is that the latter has useful hooks in judiciously chosen places. Both may do the original job about equally well, but the one with the hooks is much more flexible for future expansion of capabilities.
Emacs, for example, is *all* hooks.
The term "user exit" is synonymous but much more formal and less hackish.
(1.) Heb. hah, a "ring" inserted in the nostrils of animals to which a cord was fastened for the purpose of restraining them (2 Kings 19:28; Isa. 37:28, 29; Ezek. 29:4; 38:4). "The Orientals make use of this contrivance for curbing their work-beasts...When a beast becomes unruly they have only to draw the cord on one side, which, by stopping his breath, punishes him so effectually that after a few repetitions he fails not to become quite tractable whenever he begins to feel it" (Michaelis). So God's agents are never beyond his control. (2.) Hakkah, a fish "hook" (Job 41:2, Heb. Text, 40:25; Isa. 19:8; Hab. 1:15). (3.) Vav, a "peg" on which the curtains of the tabernacle were hung (Ex. 26:32). (4.) Tsinnah, a fish-hooks (Amos 4:2). (5.) Mazleg, flesh-hooks (1 Sam. 2:13, 14), a kind of fork with three teeth for turning the sacrifices on the fire, etc. (6.) Mazmeroth, pruning-hooks (Isa. 2:4; Joel 3:10). (7.) 'Agmon (Job 41:2, Heb. Text 40:26), incorrectly rendered in the Authorized Version. Properly a rush-rope for binding animals, as in Revised Version margin.