使用Clojure Spec从递归定义生成 [英] Generating from recursive definitions with Clojure Spec

问题描述

让我们考虑打Clo语法的Clojure Spec正则表达式

Let's consider a Clojure Spec regexp for hiccup syntax

(require '[clojure.spec :as spec])

(spec/def ::hiccup
  (spec/cat :tag        keyword?
            :attributes (spec/? map?)
            :content    (spec/* (spec/or :terminal string?
                                         :element  ::hiccup))))

精彩

(spec/conform ::hiccup [:div#app [:h5 {:id "loading-message"} "Connecting..."]])
; => {:tag :div#app, :content [[:element {:tag :h5, :attributes {:id "loading-message"}, :content [[:terminal "Connecting..."]]}]]}

直到您尝试根据规范为函数生成一些示例数据

until you try to generate some example data for your functions from the spec

(require '[clojure.spec.gen :as gen])
(gen/generate (spec/gen ::hiccup))
; No return value but:
; 1. Unhandled java.lang.OutOfMemoryError
;    GC overhead limit exceeded

是否可以重写规范以使其生成有效的生成器？还是我们必须在规范中附加一些简化的生成器？

Is there a way to rewrite the spec so that it produces a working generator? Or do we have to attach some simplified generator to the spec?

推荐答案

spec / *的意图recursion-limit * （默认值为4）是为了限制递归生成，使其可以正常工作。因此，要么在某些规范提示（ * 或或）之一中无法正常工作，要么您看到了快速增长在其他内容中（例如 map？或字符串）。不做任何修改，很难知道是什么问题。

The intent of spec/*recursion-limit* (default 4) is to limit recursive generation such that this should work. So either that's not working properly in one of the spec impls (* or or), or you are seeing rapid growth in something else (like map? or the strings). Without doing some tinkering, it's hard to know which is the problem.

这确实为我产生了（一个非常大的例子）：

This does generate (a very large example) for me:

(binding [spec/*recursion-limit* 1] (gen/generate (spec/gen ::hiccup)))

我确实看到了几个基数很大的区域，即使在一个例子中- * 和生成的属性 map的大小？。两者都可能受到进一步限制。将这些部分进一步细分为更细粒度的规范，并在必要时提供覆盖生成器将是最容易的（属性映射只能使用 map-of 和：gen-max ）。

I do see several areas where the cardinalities are large even in that one example - the * and the size of the generated attributes map?. Both of those could be further constrained. It would be easiest to break these parts up further into more fine-grained specs and supply override generators where necessary (the attribute map could just be handled with map-of and :gen-max).

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