Filesystem

Attempt to transform a Dhall record into a directory tree where:

• Records are translated into directories
• Maps are also translated into directories
• Text values or fields are translated into files
• Optional values are omitted if None

For example, the following Dhall record:

{ dir = { `hello.txt` = "Hello\n" }
, `goodbye.txt`= Some "Goodbye\n"
, `missing.txt` = None Text
}

... should translate to this directory tree:

$ tree result
result
├── dir
│   └── hello.txt
└── goodbye.txt

$ cat result/dir/hello.txt
Hello

$ cat result/goodbye.txt
Goodbye

Use this in conjunction with the Prelude's support for rendering JSON/YAML in "pure Dhall" so that you can generate files containing JSON. For example:

let JSON =
      https://prelude.dhall-lang.org/v12.0.0/JSON/package.dhall sha256:843783d29e60b558c2de431ce1206ce34bdfde375fcf06de8ec5bf77092fdef7

in  { `example.json` =
        JSON.render (JSON.array [ JSON.number 1.0, JSON.bool True ])
    , `example.yaml` =
        JSON.renderYAML
          (JSON.object (toMap { foo = JSON.string "Hello", bar = JSON.null }))
    }

... which would generate:

$ cat result/example.json
[ 1.0, true ]

$ cat result/example.yaml
! "bar": null
! "foo": "Hello"

This utility does not take care of type-checking and normalizing the provided expression. This will raise a FilesystemError exception upon encountering an expression that cannot be converted as-is.

This error indicates that you supplied an invalid Dhall expression to the directoryTree function. The Dhall expression could not be translated to a directory tree.