Original Summary

Raymond Smullyan’s &quot;To Mock a Mockingbird&quot; book&#x27;s aviary of combinator birds implemented in APL-derived languages and the problem implementing the Sage bird (Fixed Point or Y combinator) in an eagerly evaluated language.<p>Newer APLs support lazy evaluation. My eager language has a workaround for this. The Z combinator is the standard strict-language fix: wrap the self-application in one extra function layer (λv. x x v), so the recursion is a value (a delayed call) rather than an executing expression. sw-MLPL expresses that delay as a named partial — z_step&#x2F;z_recur&#x2F;applicative_sage — because the language has no anonymous lambdas.<p>Z has no Smullyan name (and no zebra in the aviary, despite the letter). The book predates and ignores the strictness problem, so it has no applicative-order variant. &quot;Z combinator&quot; is programmer folklore for the eta-expanded Y

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  • 发布时间：2026/9/22 02:03:58