What I changed on https://nim-lang.org/docs/manual.html#implementation-specific-pragmas-importobjc-pragma to get it to work on my mac

change.diff

--- /tmp/orig.nim	2018-10-24 09:01:22.000000000 -0600
+++ /tmp/frommanual.nim	2018-10-24 09:00:51.000000000 -0600
@@ -1,7 +1,6 @@
-{.passL: "-lobjc".}
 {.emit: """
-#include <objc/Object.h>
-@interface Greeter:Object
+#include <Cocoa/Cocoa.h>
+@interface Greeter:NSObject
 {
 }
 
@@ -21,12 +20,10 @@
 """.}
 
 type
-  Id {.importc: "id", header: "<objc/Object.h>", final.} = distinct int
+  Id {.importc: "id", header: "<Cocoa/Cocoa.h>", final.} = distinct int
 
 proc newGreeter: Id {.importobjc: "Greeter new", nodecl.}
 proc greet(self: Id, x, y: int) {.importobjc: "greet", nodecl.}
-proc free(self: Id) {.importobjc: "free", nodecl.}
 
 var g = newGreeter()
 g.greet(12, 34)
-g.free()