dhall - 如何创建具有任意键但键入值的 dhall 模式？

Question

在 dhall 中，如何为以下 yaml 创建架构？

environment:
    local:
        path: "/path/to/env"
        envvars:
            - var1
            - var2
    stage:
        path: "/path/to/env"
        envvars:
            - var1
            - var2
    prod:
        path: "/path/to/env"
        envvars:
            - var1
            - var2

如您所见，它具有任意键(“local”、“stage”等)但值的类型相同。我相信这是一个相当常见的用例，但我没有在教程中看到它的讨论。

Answer 1

您可以在 Prelude 中使用 Map 、 defined ，在 Language Tour 中使用 discussed 。

let Prelude = http://prelude.dhall-lang.org/v16.0.0/package.dhall

let Environment = { path : Text, envvars : List Text }

let EnvironmentSet = { environment : Prelude.Map.Type Text Environment }

in    { environment = toMap
          { local = { path = "/path/to/env", envvars = [ "var1", "var2" ] }
          , stage = { path = "/path/to/env", envvars = [ "var1", "var2" ] }
          , prod = { path = "/path/to/env", envvars = [ "var1", "var2" ] }
          }
      }
    : EnvironmentSet

dhall-to-yaml 生成原始 YAML(模键顺序):

% dhall-to-yaml < tmp.dhall
environment:
  local:
    envvars:
      - var1
      - var2
    path: /path/to/env
  prod:
    envvars:
      - var1
      - var2
    path: /path/to/env
  stage:
    envvars:
      - var1
      - var2
    path: /path/to/env

您还可以通过定义一些函数来创建记录和映射来摆脱大部分样板文件。

let Map = http://prelude.dhall-lang.org/v16.0.0/Map/package.dhall

let Environment = { path : Text, envvars : List Text }

let makeEnv =
        λ(name : Text)
      → λ(path : Text)
      → λ(vars : List Text)
      → Map.keyValue Environment name { path = path, envvars = vars }

let makeEnvironmentSet =
      λ(envs : List (Map.Entry Text Environment)) → { environment = envs }

in  makeEnvironmentSet
      [ makeEnv "local" "/path/to/local" [ "localvar1", "localvar2" ]
      , makeEnv "stage" "/path/to/stage" [ "stagevar1", "stagevar2" ]
      , makeEnv "prod" "/path/to/prod" [ "prodvar1", "prodvar2" ]
      ]

dhall-to-yaml 将 {mapKey: k, mapValue: v} 类型的记录转换为 YAML 对象。