Equivalent of Format-Table

Format-Table in PowerShell

In PowerShell, if I have a list of objects:

$items = @(
    [pscustomobject]@{ a = 10;   b = 20;    c = "bcd" }
    [pscustomobject]@{ a = 300;  b = 400;   c = "bcde" }
    [pscustomobject]@{ a = 5000; b = 60000; c = "bcdef" }
) 

I can display the objects as a table:

$items | Format-Table

The result:

   a     b c
   -     - -
  10    20 bcd
 300   400 bcde
5000 60000 bcdef

F#

If I have a similar list in F#:

type Abc = {
    a : int
    b : int
    c : string
}

let items = [
    { a = 10; b = 20; c = "bcd" }
    { a = 300; b = 400; c = "bcde" }
    { a = 5000; b = 60000; c = "bcdef" }
] 

I have to be more explicit if I want to display a similar table:

items |> List.iter (fun item -> printfn "%10d %10d %s" item.a item.b item.c) 

format_table function

Here's a format_table function (which uses Fli):

let format_table seq =
    let json = JsonSerializer.Serialize seq
    System.IO.File.WriteAllText("c:/temp/out.json", json)
    let result_cli = (cli {
        Shell PS
        Command "Get-Content c:\\temp\\out.json | ConvertFrom-Json | Format-Table"
    } |> Command.execute)

    match result_cli.Text with
    | Some(txt) -> printfn "%s" txt
    | None -> printfn "issue"

So I can do:

items |> format_table

and get:

   a     b c
   -     - -
  10    20 bcd
 300   400 bcde
5000 60000 bcdef

Question

As you can see, format_table is quite the workaround:

• It serializes the list to JSON
• It writes the JSON to a temporary file
• It executes PowerShell which uses Format-Table on the data

Is there a straightforward way to write something similar to format_table without depending on an external PowerShell process?

Here is a simple version, using reflection.

open System.Reflection
open FSharp.Reflection

let printTable items =
    let genArgs = items.GetType().GenericTypeArguments
    assert (genArgs.Length = 1)
    let itemType = genArgs[0]
    assert (FSharpType.IsRecord itemType)
    let fieldNames = FSharpType.GetRecordFields itemType |> Array.map (fun propInfo -> propInfo.Name)
    printfn $"""{fieldNames |> Array.map (sprintf "%10s") |> String.concat ""}"""
    printfn $""" {Array.replicate fieldNames.Length "_________" |> String.concat " "}"""
    let printFields item =
        let fields =  FSharpValue.GetRecordFields item
        printfn $"""{fields |> Array.map (string >> sprintf "%10s") |> String.concat ""}"""
    items |> Seq.iter printFields