dh_haskell_provides: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/dh_haskell_provides - from package: haskell-devscripts

You may install the required package with command apt-get install {package}

Error in other languages:
dh_haskell_provides: bevel nie gevind nie
dh_haskell_provides: comandă negăsită
dh_haskell_provides: comando não encontrado
dh_haskell_provides: commande introuvable
dh_haskell_provides: command not found
dh_haskell_provides: käsku ei ole
dh_haskell_provides: không tìm thấy lệnh
dh_haskell_provides: komanda nerasta
dh_haskell_provides: Kommando nicht gefunden.
dh_haskell_provides: kommandot finns inte
dh_haskell_provides: komut yok
dh_haskell_provides: nie znaleziono polecenia
dh_haskell_provides: níor aimsíodh an t-ordú
dh_haskell_provides: no se encontró la orden
dh_haskell_provides: no s'ha trobat l'ordre
dh_haskell_provides: opdracht niet gevonden
dh_haskell_provides: parancs nem található
dh_haskell_provides: perintah tidak ditemukan
dh_haskell_provides: príkaz nenájdený
dh_haskell_provides: příkaz nenalezen
dh_haskell_provides: команда не найдена
dh_haskell_provides: командата не е открита
dh_haskell_provides: 命令找不到
dh_haskell_provides: コマンドが見つかりません