String Functions in F#

Our first program demonstrates various string operations using F#’s built-in String module. Here’s the full source code:

open System

// We alias printfn to a shorter name as we'll use it a lot below.
let p = printfn

[<EntryPoint>]
let main argv =
    // Here's a sample of the functions available in the String module.
    // Since these are functions from the module, not methods on the string
    // object itself, we need to pass the string in question as the first
    // argument to the function. You can find more functions in the
    // String module documentation.

    p "Contains:  %b" (String.contains "es" "test")
    p "Count:     %d" (Seq.filter ((=) 't') "test" |> Seq.length)
    p "StartsWith: %b" (String.startsWith "te" "test")
    p "EndsWith:  %b" (String.endsWith "st" "test")
    p "IndexOf:   %d" ("test".IndexOf('e'))
    p "Join:      %s" (String.concat "-" ["a"; "b"])
    p "Repeat:    %s" (String.replicate 5 "a")
    p "Replace:   %s" ("foo".Replace("o", "0"))
    p "Replace:   %s" ("foo".Replace("o", "0", 1, System.StringComparison.Ordinal))
    p "Split:     %A" ("a-b-c-d-e".Split('-'))
    p "ToLower:   %s" (String.lowercase "TEST")
    p "ToUpper:   %s" (String.uppercase "test")
    0

To run the program, save the code in a file with a .fs extension (e.g., StringFunctions.fs) and use the F# compiler (fsc) to compile it, then run the resulting executable:

$ fsharpc StringFunctions.fs
$ mono StringFunctions.exe
Contains:  true
Count:     2
StartsWith: true
EndsWith:  true
IndexOf:   1
Join:      a-b
Repeat:    aaaaa
Replace:   f00
Replace:   f0o
Split:     [|"a"; "b"; "c"; "d"; "e"|]
ToLower:   test
ToUpper:   TEST

This example demonstrates various string operations in F#. Note that F# provides both functions in the String module and instance methods on string objects, giving you flexibility in how you work with strings.

F# doesn’t have a direct equivalent to Go’s strings package, but it provides similar functionality through the String module and instance methods on strings. Some operations, like Count, are implemented using more general sequence operations in F#.

The String module in F# provides many useful string-related functions. You can find more functions in the String module documentation.

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String Functions in F#