[SOLVED] ComboBox in Gtk2hs compiling error

ComboBox in Gtk2hs compiling error

How can I handle a ComboBox with Gtk2hs? On this page I found a solution:

store <- listStoreNew ["green", "yellow", "..."]
comboElem <- comboBoxNewWithModel store
ren <- cellRendererTextNew
cellLayoutPackEnd comboElem ren True
cellLayoutSetAttributes comboElem ren store
  (\txt -> [cellText := Just txt])

However while compiling I get this error (which occurs in the last line of my code example):

Main.hs:36:17:
No instance for (System.Glib.UTFString.GlibString (Maybe [Char]))
  arising from a use of ‘cellText’
In the first argument of ‘(:=)’, namely ‘cellText’
In the expression: cellText := Just txt
In the expression: [cellText := Just txt]

How can I fix the problem?

Thanks in advance

Solution

GlibString Doesn't appear to have an instance for Maybe String. It may have at one point, but you should be able to just use cellText := txt instead. If for whatever reason you need to use a Maybe String, you could implement the instance yourself.