Xah Talk Show 2025-12-29 Ep735 Learning Fsharp by Asking AI. Write a Find Replace Script

in fsharp, how to read a file as string

// 2025-12-29
// read file into a string

open System.IO

let xfilePath = @"c:/Users/xah/web/xahlee_info/talk_show/xah_talk_show_ep735.html"
  // Use @ for verbatim strings or escape backslashes
let content: string = File.ReadAllText(xfilePath)

printfn "%s" content

in fsharp, how to write to a file

// 2025-12-29
// write a string to a file

open System.IO

let content = "hi there beautiful."

File.WriteAllText("output.txt", content)

how to print in fsharp

printf "Hello, "
printf "world!"

printfn ""  // Adds a newline for clean output

printfn "Hello, world!"

in fsharp, how to replace string

// 2025-12-29
// replace string

let xoriginal = "something in the water."

let xreplaced = xoriginal.Replace("water", "fire")

printfn "%s" xreplaced
// something in the fire.

// s------------------------------

// replace a char

let xreplacedChar = xoriginal.Replace('o', 'a')   // Replaces single char
printfn "%s" xreplacedChar
// samething in the water.

in fsharp, how to list dir content

// 2025-12-29
// list dir content

open System.IO

let xpath = @"c:/Users/xah/web/xahlee_info/talk_show/"
// or "." for current directory

let files = Directory.GetFiles(xpath)  // Returns string[] of full paths

// s------------------------------

// Or lazily (better for large directories):
let filesSeq = Directory.EnumerateFiles(xpath)  // Returns seq<string>

// Print them
filesSeq |> Seq.iter (printfn "%s")

// s------------------------------

// With a pattern, e.g., only .txt files:
Directory.EnumerateFiles(xpath, "*.txt") |> Seq.iter (printfn "%s")

in fsharp, how to list dir content and all subdirs

open System.IO

let xpath = "c:/Users/xah/web/xahlee_info/talk_show/"

// All files recursively
Directory.EnumerateFiles(xpath, "*.*", SearchOption.AllDirectories)
|> Seq.iter (printfn "%s")

// Or with DirectoryInfo
// dirInfo.EnumerateFiles("*.*", SearchOption.AllDirectories)
// |> Seq.iter (fun fi -> printfn "%s" fi.FullName)

in fsharp, why open System.IO not import or require