runhaskell-ghc: 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/runhaskell-ghc - from package: ghc-compiler

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

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