haddock: 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 CentOS possible default full paths are:

/usr/bin/haddock - from package: ghc-compiler

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/haddock - from package: ghc-haddock

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

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