Above all the wonders of Lisp’s pantheon stand its metalinguistic tools; by their grace have Lisp’s acolytes been liberated from the rigid asceticism of lesser faiths. Thanks to Macro and kin, the jolly, complacent Lisp hacker can gaze through a fragrant cloud of setfs and defstructs at the emaciated unfortunates below, scraping out their meager code in inflexible notation, and sneer superciliously. It’s a good feeling.

But all’s not joy in Consville. For—I beg your pardon, but—there really is no good way to iterate in Lisp. Now, some are happy to map their way about, whether for real with mapcar and friends, or with the make-believe of Series; others are so satisfied with do it’s a wonder they’re not C hackers.1 Still others have gotten by with loop, but are getting tired of looking up the syntax in the manual over and over again. And in the elegant schemes of some, only tail recursion and lambdas figure. But that still leaves a sizeable majority of folk—well, me, at least—who would simply like to iterate, thank you, but in a way that provides nice abstractions, is extensible, and looks like honest-to-God Lisp.

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