Difference between param and function syntax in PowerShell - function

Question

In PowerShell I can pass a parameter if I create a closure with param syntax:
$hello = { param($name) "Hello $name"}
& $hello "World!"
>hello.ps1
Hello World!
When I try this with function syntax I get into trouble:
function hello($n) { { "Hello $n" }.GetNewClosure() }
$doit = hello
& $doit "World!"
>functionclosure.ps1
Hello
I managed to fix this by giving the parameter earlier:
function hello($n) { {"Hello $n"}.GetNewClosure() }
$doit = hello "World"
& $doit
>functionclosure2.ps1
Hello World
Is there a way to pass a parameter to a function from the & call operator line?

Answer 1

Is there a way to pass a parameter to a function from the & call operator line?
The call (also known as invocation or &) operator is generally used to execute content in a string, which we do when there is a long file path or a path with spaces in the name, or when we are dynamically building a string to execute.
Now, in this case, Using GetNewClosure() alters a function to instead return a scriptblock as the output type. That Scriptblock must be invoked using the Call operator, so this is a valid usage of the Call operator.
Back to your question then, yes, you can control the order of execution using paranthesis and pass a parameter to a function which returns a closure from the call line like this:
& (hello stephen)
However, this is pretty confusing in action as closures maintain their own separate scope and in more than ten years of enterprise automation projects, I never saw them used. It might be more confusion than it's worth to go down this route.
Prehaps a simpler approach might be:
function hello($name) { "WithinFunction: Hello $name"}
$do = 'hello "world"'
PS> $do
hello "world"
#invoke
PS> invoke-expression $do
WithinFunction: Hello world
Additional reading on closures by the man himself who implemented it in PowerShell here. https://devblogs.microsoft.com/scripting/closures-in-powershell/

Answer 2

Jeroen Mostert wrote this as a comment:
You've written a function that takes a parameter and then creates a closure using that parameter. It seems like you want a function that returns a closure that takes a parameter -- but that's the same as your first example, and
function hello { { param($n) "Hello $n"} }
would do that. You'd invoke that as
& (hello) "world"
On the other hand, if you want to have a function as a closure you can invoke,
${function:hello}
would do that, i.e.
function hello($n) { "Hello $n" };
$doit = ${function:hello};
& $doit "World"