Directories in F#

Here’s the translation of the Go code to F# with explanations in Markdown format suitable for Hugo:

Our first program will demonstrate how to work with directories in F#. We’ll use the System.IO namespace, which provides various functions for file and directory operations.

open System
open System.IO

// Helper function to check for errors
let check (result: Result<unit, exn>) =
    match result with
    | Ok _ -> ()
    | Error e -> raise e

// Helper function to create an empty file
let createEmptyFile (name: string) =
    File.WriteAllText(name, "")

// Main function
let main() =
    // Create a new sub-directory in the current working directory
    Directory.CreateDirectory("subdir") |> ignore

    // When creating temporary directories, it's good practice to ensure their removal
    // We'll use a try-finally block to ensure cleanup
    try
        // Create files and directories
        createEmptyFile "subdir/file1"
        
        // Create a hierarchy of directories
        Directory.CreateDirectory("subdir/parent/child") |> ignore
        
        createEmptyFile "subdir/parent/file2"
        createEmptyFile "subdir/parent/file3"
        createEmptyFile "subdir/parent/child/file4"

        // List directory contents
        let parentContents = Directory.GetFileSystemEntries("subdir/parent")
        
        printfn "Listing subdir/parent"
        for entry in parentContents do
            let isDirectory = Directory.Exists(entry)
            printfn " %s %b" (Path.GetFileName(entry)) isDirectory

        // Change the current working directory
        Directory.SetCurrentDirectory("subdir/parent/child")

        // List contents of the current directory
        let currentContents = Directory.GetFileSystemEntries(".")
        
        printfn "Listing subdir/parent/child"
        for entry in currentContents do
            let isDirectory = Directory.Exists(entry)
            printfn " %s %b" (Path.GetFileName(entry)) isDirectory

        // Change back to the original directory
        Directory.SetCurrentDirectory("../../..")

        // Recursively visit all files and directories
        let rec visitDir (dir: string) =
            printfn " %s %b" dir true
            for entry in Directory.GetFileSystemEntries(dir) do
                if Directory.Exists(entry) then
                    visitDir entry
                else
                    printfn " %s %b" entry false

        printfn "Visiting subdir"
        visitDir "subdir"

    finally
        // Clean up: remove the created directory and all its contents
        Directory.Delete("subdir", true)

// Run the main function
main()

To run the program, save it as Directories.fs and use the F# compiler:

$ fsharpc Directories.fs
$ mono Directories.exe
Listing subdir/parent
 child True
 file2 False
 file3 False
Listing subdir/parent/child
 file4 False
Visiting subdir
 subdir True
 subdir/file1 False
 subdir/parent True
 subdir/parent/child True
 subdir/parent/child/file4 False
 subdir/parent/file2 False
 subdir/parent/file3 False

This F# program demonstrates various directory operations:

Creating directories and files
Listing directory contents
Changing the current working directory
Recursively visiting a directory structure

The program uses functions from the System.IO namespace to perform these operations. Note that F# uses a different approach for error handling and resource management compared to Go. We use a try-finally block to ensure cleanup, and pattern matching for error checking.

The visitDir function demonstrates a recursive approach to directory traversal, which is equivalent to Go’s filepath.WalkDir.

Remember to handle exceptions and clean up resources properly when working with file systems in real-world applications.

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Directories in F#