Problem Statement

Quoting from the Esolangs wiki page: For concreteness, in this task we shall assume that symbol = character. The narcissist should be able to cope with any finite input, whatever its length. Any form of output is allowed, as long as the program always halts, and "accept", "reject" and "not yet finished" are distinguishable.

Let's start with the solution:

function Narcissist
{
Param ( [string]$String )
If ( $String -eq $MyInvocation.MyCommand.Definition ) { 'Accept' }
Else { 'Reject' }
}


Narcissist 'Banana'
 
Narcissist @'

Param ( [string]$String )
If ( $String -eq $MyInvocation.MyCommand.Definition ) { 'Accept' }
Else { 'Reject' }

'@