如何在 dhall 中模拟 Python join 函数？

Question

我是 dhall 的新手，没有 Haskell 背景。如何将字符串列表转换为值以逗号分隔的单个字符串？例如

["a", "b", "c"] -> "a,b,c"

我尝试了 List/fold，但无法找到摆脱多余逗号的惯用方法。

谢谢

Answer 1

除非有人提供更好的答案，否则以下似乎有效：

\(xs: List Text) ->
    let b = {index: Natural, value: Text}
    let ys = List/indexed Text xs
    let dlm = \(i: Natural) -> if Natural/isZero i then "" else ","
in List/fold b ys Text (\(x: b) -> \(y: Text) -> "${dlm x.index}${x.value}${y}") ""

Answer 2

Prelude 有一个 Text/concatSep 功能，这就是您要找的：

let Text/concatSep = https://prelude.dhall-lang.org/Text/concatSep

in  Text/concatSep "," [ "a", "b", "c" ]

这是源代码，如果您对它的实现方式感兴趣的话：

Prelude - Text/concatSep

如何在 dhall 中模拟 Python join 函数？

how to emulate Python join function in dhall?

dhall