add yank functionality in imperative shell

ffi/glfw-export.c

@@ -41,3 +41,8 @@ void swapBuffers(GLFWwindow *window) {
   glfwSwapBuffers(window);
 }
 
+void setClipboardString (GLFWwindow *window, const char *copyString) {
+  glfwSetClipboardString(window, copyString);
+  printf("ddone yanking");
+}
+

ffi/glfw-import.sml

@@ -22,4 +22,5 @@ struct
   val windowShouldClose = _import "windowShouldClose" public : window -> bool;
   val waitEvents = _import "waitEvents" public reentrant : unit -> unit;
   val swapBuffers = _import "swapBuffers" public : window -> unit;
+  val setClipboardString = _import "setClipboardString" public : window * string -> unit;
 end