How do you associate a button with a callback?

import fltk as fl

var btn = make_button(64, 64, 100, 64, "Click!")

btn.box = fl.Up_box
btn.labelfont = fl.Helvetica
#btn.labelsize = 12
btn.labeltype = fl.Normal_label


var win = make_window(320, 240, "Test window.")
win.labelfont = fl.Helvetica
win.labelsize = 12

win.begin()
win.add btn
win.endd()
win.show(0, nil)

proc cb(x: int) = 
    echo ("Hello")

discard fl.run()

nim cpp test.nim returns
Hint: used config file '/usr/local/etc/nim/nim.cfg' [Conf]
........
/usr/home/x/Dirs/Src/Nim/nfltk/private/image.nim(83, 22) Warning: use csize_t instead; csize is deprecated [Deprecated]
/usr/home/x/Dirs/Src/Nim/nfltk/private/image.nim(84, 19) Warning: use csize_t instead; csize is deprecated [Deprecated]
/usr/home/x/Dirs/Src/Nim/nfltk/private/widget.nim(10, 18) Warning: use csize_t instead; csize is deprecated [Deprecated]
/usr/home/x/Dirs/Src/Nim/nfltk/private/widget.nim(11, 19) Warning: use csize_t instead; csize is deprecated [Deprecated]
/usr/home/x/Dirs/Src/Nim/nfltk/private/widget.nim(10, 18) Warning: use csize_t instead; csize is deprecated [Deprecated]
/usr/home/x/Dirs/Src/Nim/nfltk/private/widget.nim(11, 19) Warning: use csize_t instead; csize is deprecated [Deprecated]
...
/usr/home/x/Dirs/Src/Nim/nfltk/private/input.nim(113, 40) Warning: use csize_t instead; csize is deprecated [Deprecated]
.................CC: stdlib_system.nim
CC: private/enumerations.nim
CC: private/nimwidget.nim
CC: test.nim
/home/x/.cache/nim/test_d/@[email protected]:32:1: error: visibility does not match previous declaration
N_LIB_PRIVATE Fl_Fontsize FL_NORMAL_SIZE;
^
/usr/local/lib/nim/nimbase.h:194:40: note: expanded from macro 'N_LIB_PRIVATE'

define N_LIB_PRIVATE attribute((visibility("hidden")))

                                   ^

/usr/local/include/FL/Enumerations.H:906:8: note: previous attribute is here
extern FL_EXPORT Fl_Fontsize FL_NORMAL_SIZE; ///< normal font size
^
/usr/local/include/FL/Fl_Export.H:33:39: note: expanded from macro 'FL_EXPORT'

define FL_EXPORT attribute ((visibility ("default")))

                                  ^

1 error generated.

Error: execution of an external compiler program 'clang++ -c -std=gnu++14 -funsigned-char -I/usr/local/lib/nim -I/usr/local/include -I/usr/local/include -I/usr/home/x/Dirs/Src/Nim/nfltk -o /home/x/.cache/nim/test_d/@[email protected] /home/x/.cache/nim/test_d/@[email protected]' failed with exit code: 1

HOST:x: /home/x/Dirs/Src/Nim/nfltk >

Installation:

serge@DESKTOP-K41AO9P MINGW64 /c/Users/serge/Documents/vue-tests/vue-tests-nomodules/Julia-1-rust-python-wordcount
$ nimble install fltk
Downloading https://github.com/Skrylar/nfltk using git
  Verifying dependencies for [email protected]
 Installing [email protected]
    Prompt: [email protected] already exists. Overwrite? [y/N]
y
    Answer:    Success: fltk installed successfully.

Attempt to use:

serge@DESKTOP-K41AO9P MINGW64 /c/Users/serge/Documents/vue-tests/vue-tests-nomodules/Julia-1-rust-python-wordcount
$ nim cpp fltk_1.nim
Hint: used config file 'C:\Users\serge\Documents\vue-tests\vue-tests-nomodules\Nim\config\nim.cfg' [Conf]
Hint: used config file 'C:\Users\serge\Documents\vue-tests\vue-tests-nomodules\Nim\config\config.nims' [Conf]
....
C:\Users\serge\Documents\vue-tests\vue-tests-nomodules\Julia-1-rust-python-wordcount\fltk_1.nim(1, 13) Error: cannot open file: fltk

serge@DESKTOP-K41AO9P MINGW64 /c/Users/serge/Documents/vue-tests/vue-tests-nomodules/Julia-1-rust-python-wordcount

Hi,
By default FLTK library is linked dynamically. How can I create a statically linked image of my nim program?
Thanks

there are so many such out in different files