我应该在clojure中实现Seq接口 [英] Should I implement the Seq interface in clojure

问题描述

我在Clojure中有一个数据结构，它表示一组实验的结果：

I have a data structure in Clojure which represents a set of results from an experiment:

(defprotocol ResultSet
  (columns [rs] "return a collection of the columns in the resultset, represented by keywords")
  (rows [rs] [rs column-keys] "returns a seq of the rows in the resultset, order and column specified as keywords by column-keys. with a single argument returns rows with all columns present"))

我有一个 deftype ，它实现了这个协议。我感兴趣的是编写函数，这些函数将函数映射到结果集中的所有结果，或者折叠结果集，基本上做与内置seq函数相同的事情。

And I have a deftype which implements this protocol. I am interested in writing functions which do things like map a function over all the results in the resultset, or which fold over the result set, basically doing the same things as the built in seq functions.

在Haskell中，我将通过实现相关类型类（如Functor）然后使用fmap或mfilter等函数来实现。所以我在Clojure中做了这件事，结束了关于实现ISeq接口的一些想法。

In Haskell I would do this by implementing the relevant typeclasses (eg Functor) and then using functions like fmap or mfilter. So I looked into doing this in Clojure and wound up with some ideas about implementing the ISeq interface.

那么，这是个好主意吗？我找不到很多关于实现ISeq的资源，我想知道这是什么惯用的方法。

So, is this a good idea? I can't find many resources about implementing ISeq and I am wondering what the idiomatic approach to this is.

推荐答案

我可以告诉，最好的实现这样的东西不是实现ISeq，而是clojure.lang.Seqable;换句话说，提供（.seq）的实现，以将ResultSet映射到（可能是延迟的）序列。这是路由clojure用于大多数（所有？）集合，除了list（列表实现ISeq，因为seq API已经是列表API的一个子集）。

As far as I can tell, the "best" way to implement something like this is not to implement ISeq, but clojure.lang.Seqable; in other words, provide an implementation of (.seq) to map your ResultSet to a (possibly lazy) sequence. That is the route clojure uses for most (all?) collections except list (lists implement ISeq, because the seq API is already a subset of the list API).

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