Allow tab for selection completion in deoplete

after/ftplugin/haskell.vim

@@ -75,8 +75,10 @@ call deoplete#custom#option('sources',{
 	\ '_': ['buffer'],
 	\ 'haskell': ['ultisnips', 'buffer', 'file', 'LanguageClient']
 	\ })
+inoremap <expr><tab> pumvisible() ? "\<c-n>" : "\<tab>"
 call deoplete#enable()
 
+
 let g:ghcmod_hlint_options = ['--ignore=Eta reduce $']
 
 " ALE