fsyacc: 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/fsyacc - from package: fsharp

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

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