ml-yacc: 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/ml-yacc - from package: ml-yacc
/usr/lib/smlnj/bin/ml-yacc - from package: ml-yacc

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

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