Logging in F#

Here’s the translation of the Go logging example to F#, formatted in Markdown suitable for Hugo:

open System
open System.IO

// The F# equivalent of the standard logger is to use printfn
printfn "standard logger"

// In F#, we don't have flags for logging, but we can create custom formatting
let logWithTime message =
    printfn "%s %s" (DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.ffffff")) message

logWithTime "with micro"

// To include file and line information, we can use caller information attributes
let logWithFileAndLine ([<CallerFilePath>] ?filePath: string) ([<CallerLineNumber>] ?lineNumber: int) message =
    let file = Path.GetFileName(defaultArg filePath "")
    let line = defaultArg lineNumber 0
    printfn "%s %s:%d: %s" (DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss")) file line message

logWithFileAndLine "with file/line"

// Custom loggers in F# can be implemented as functions
let mylog prefix message =
    printfn "%s%s %s" prefix (DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss")) message

mylog "my:" "from mylog"
mylog "ohmy:" "from mylog"

// Logging to a custom target (like a string buffer)
let logToBuffer (buffer: StringWriter) prefix message =
    buffer.WriteLine(sprintf "%s%s %s" prefix (DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss")) message)

let buffer = new StringWriter()
logToBuffer buffer "buf:" "hello"
printfn "from buflog:%s" (buffer.ToString())

// For structured logging, we can use a third-party library like Serilog
// Here's a simple example of how it might look:
(*
#r "nuget: Serilog"
#r "nuget: Serilog.Sinks.Console"

open Serilog

Log.Logger <- LoggerConfiguration()
                .WriteTo.Console()
                .CreateLogger()

Log.Information("hi there")
Log.Information("hello again {Key} {Age}", "val", 25)
*)

// Since F# is part of the .NET ecosystem, you might also use the built-in ILogger interface
// Here's a simple example:
open Microsoft.Extensions.Logging

let factory = LoggerFactory.Create(fun builder ->
    builder.AddConsole() |> ignore
)
let logger = factory.CreateLogger<obj>()

logger.LogInformation("hi there")
logger.LogInformation("hello again {Key} {Age}", "val", 25)

This F# code demonstrates logging capabilities similar to those in the original Go example. Here’s a breakdown of the translation:

We use printfn as a simple equivalent to Go’s standard logger.
Custom formatting for timestamps is implemented using a custom function logWithTime.
File and line information is added using F#’s caller information attributes.
Custom loggers are implemented as functions that take a prefix and a message.
Logging to a custom target (like a string buffer) is demonstrated using a StringWriter.
For structured logging, we show two options:
- Serilog, a popular third-party logging library (commented out as it requires additional setup).
- .NET’s built-in ILogger interface, which provides structured logging capabilities.

Note that F# and .NET have different logging paradigms compared to Go, so some concepts are adapted or replaced with similar functionality. The structured logging example using ILogger is the closest equivalent to Go’s slog package in terms of functionality.

To run this program, save it as a .fsx file and use the F# Interactive (FSI) or compile it as a regular F# program. The output will be similar to the Go version, with timestamps and structured log entries.

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Logging in F#