File Paths in Elm

The String module in Elm provides functions to work with strings, which we can use to manipulate file paths. However, Elm doesn’t have a direct equivalent to Go’s filepath package, so we’ll focus on string manipulation for file paths.

import String

main =
    let
        -- Join should be used to construct paths in a portable way.
        -- It takes any number of arguments and constructs a hierarchical path from them.
        p = String.join "/" ["dir1", "dir2", "filename"]
    in
    String.join "\n"
        [ "p: " ++ p
        , "Join example: " ++ String.join "/" ["dir1//", "filename"]
        , "Join with .. example: " ++ String.join "/" ["dir1", "..", "dir1", "filename"]
        , "Dir(p): " ++ (p |> String.split "/" |> List.dropRight 1 |> String.join "/")
        , "Base(p): " ++ (p |> String.split "/" |> List.reverse |> List.head |> Maybe.withDefault "")
        , "IsAbs(dir/file): " ++ (String.startsWith "/" "dir/file" |> Debug.toString)
        , "IsAbs(/dir/file): " ++ (String.startsWith "/" "/dir/file" |> Debug.toString)
        ]
        |> Debug.log "Output"

-- Some file operations
filename = "config.json"

-- We can split the extension out of such names
ext = 
    filename 
        |> String.split "." 
        |> List.reverse 
        |> List.head 
        |> Maybe.withDefault ""
        |> (++) "."

-- To find the file's name with the extension removed
nameWithoutExt =
    filename
        |> String.dropRight (String.length ext)

-- Rel finds a relative path between a base and a target
rel base target =
    let
        baseParts = String.split "/" base
        targetParts = String.split "/" target
        commonParts = List.map2 (\b t -> if b == t then Just b else Nothing) baseParts targetParts
                        |> List.takeWhile (\x -> x /= Nothing)
                        |> List.length
        upDirs = List.repeat (List.length baseParts - commonParts) ".."
        remainingTargetParts = List.drop commonParts targetParts
    in
    String.join "/" (upDirs ++ remainingTargetParts)

In this Elm code:

We use String.join "/" to join path components, simulating filepath.Join.
For Dir and Base operations, we split the path, manipulate the parts, and join them back.
IsAbs is simulated by checking if the path starts with “/”.
We extract the file extension by splitting on “.” and taking the last part.
To remove the extension, we use String.dropRight.
The rel function simulates filepath.Rel by comparing path components and constructing the relative path.

To run this program, you would typically compile it with the Elm compiler and then run it in a browser or with Node.js, as Elm is primarily designed for web applications. The output would be similar to the Go example, but keep in mind that some operations might behave differently due to the different nature of Elm and its primary use case in web development.

Remember that Elm’s standard library doesn’t include comprehensive file system operations, as it’s designed for web applications. For actual file system operations in a production environment, you would typically use JavaScript interop or create a custom element to handle these operations on the server side.

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File Paths in Elm