gistfile1.txt

[nix-shell:~/try-reflex]$ cat source.hs 
import Reflex.Dom
import Data.Default

main = mainWidget $ el "div" $ do
      t <- textInput def
      dynText $ _textInput_value t

[nix-shell:~/try-reflex]$ ghcjs source.hs 
[1 of 1] Compiling Main             ( source.hs, source.js_o )

source.hs:4:21:
    Couldn't match type ‘TextInput’
                   with ‘Widget
                           Reflex.Spider.Internal.Spider
                           (Gui
                              Reflex.Spider.Internal.Spider
                              Reflex.Spider.Internal.SpiderHost
                              (Reflex.Host.Class.HostFrame Reflex.Spider.Internal.Spider))’
    Expected type: Widget
                     Reflex.Spider.Internal.Spider
                     (Gui
                        Reflex.Spider.Internal.Spider
                        Reflex.Spider.Internal.SpiderHost
                        (Reflex.Host.Class.HostFrame Reflex.Spider.Internal.Spider))
                     ()
      Actual type: TextInput ()
    In the second argument of ‘($)’, namely
      ‘el "div"
       $ do { t <- textInput def;
              dynText $ _textInput_value t }’
    In the expression:
      mainWidget
      $ el "div"
        $ do { t <- textInput def;
               dynText $ _textInput_value t }
    In an equation for ‘main’:
        main
          = mainWidget
            $ el "div"
              $ do { t <- textInput def;
                     dynText $ _textInput_value t }

It looks like you might be building this with the master branch of try-reflex. If you delete the def, that will work; however, it's better to update try-reflex to develop.

Ok, sorry.