PowerShell ISE how to automate new tab creation with ScriptBlock closures?

Question

I'm trying to automate creation of a bunch of tabs in PowerShell ISE

I've started with a function such as

function Start-NewTab($name, [ScriptBlock]$scriptBlock)
{
    $tab = $psISE.PowerShellTabs.Add()
    $tab.DisplayName = $name
    sleep 2
    $tab.Invoke($scriptBlock)
}

however when I run it like so

$v = "hello world"
Start-NewTab "Test" { $v }

hello world isn't shown, unlike the following fragement

function Test-ScriptBlock([ScriptBlock]$sb) { & $sb }
Test-ScriptBlock { $v }

What's going on here and how do I fix it?

Answer 1

A "Tab" container is equated to a runspace (or powershell execution environment) in the ISE. Since you are creating a new Tab (i.e. powershell execution environment) the variable v is undefined in that execution environment. The scriptblock is evaluated in the new execution environment and outputs the value of v (nothing).

It's easy to see how variable resolutions differs in the case of Test-Scriptblock from the case of Start-NewTab if you try to get the variable in the scriptblock by explicitly mentioning the scope where the variable should be found.

PS>Test-ScriptBlock { get-variable v -scope 0}
Get-Variable : Cannot find a variable with name 'v'.
PS>Test-ScriptBlock { get-variable v -scope 1}
Get-Variable : Cannot find a variable with name 'v'.
PS>Test-ScriptBlock { get-variable v -scope 2} # Variable found in grandparent scope (global in the same execution environment)
Name                           Value                                                                                                                           
----                           -----                                                                                                                           
v                              hello world

PS>Start-NewTab "Test" { get-variable v -scope 0 } # global scope of new execution environment
Get-Variable : Cannot find a variable with name 'v'.
PS>Start-NewTab "Test" { get-variable v -scope 1 } # proof that scope 0 = global scope
Get-Variable : The scope number '1' exceeds the number of active scopes.

One workaround for your problem is to define your variable in the scriptblock:

Start-NewTab "Test" { $v = "hello world";$v }

Edit: One more thing, your title mentions 'closure'. Scriptblocks in Powershell are not closures, however you can create a closure from a scriptblock. This won't help you with the problem you describe, though.

Edit2: Another workaround:

$v = "hello world"
Invoke-Expression "`$script = { '$v' }"
Start-NewTab "test" $script