Can't seem to get Foundation types to work in Linux

Using Swift
1

Not sure what I'm doing wrong here, but I thought Foundation types were supported on Linux. I'm trying to make my iOS/MacOS lib Linux compatible.

$ swift -lFoundation
Welcome to Swift version 5.1.5 (swift-5.1.5-RELEASE).
Type :help for assistance.
  1> import Foundation
  2> NSString.self
error: repl.swift:2:1: error: use of unresolved identifier 'NSString'
NSString.self
^~~~~~~~

error: repl.swift:2:1: error: use of unresolved operator '=='
NSString.self
^~~~~~~~


  2> NSNumber.self
error: repl.swift:2:1: error: use of unresolved identifier 'NSNumber'
NSNumber.self
^~~~~~~~

error: repl.swift:2:1: error: use of unresolved operator '=='
NSNumber.self
^~~~~~~~


  2>
2

I cannot reproduce with the official Swift 5.1.5 or 5.2 release builds running on Arch linux, works for me.

1> import Foundation
2> NSNumber.self
$R0: NSNumber.Type = NSNumber