scheme-r4rs: 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/lib64/gambit-c/bin/scheme-r4rs - from package: gambit-c

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

On Debian possible default full paths are:

/usr/bin/scheme-r4rs - from package: gambc

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

Error in other languages:
scheme-r4rs: bevel nie gevind nie
scheme-r4rs: comandă negăsită
scheme-r4rs: comando não encontrado
scheme-r4rs: commande introuvable
scheme-r4rs: command not found
scheme-r4rs: käsku ei ole
scheme-r4rs: không tìm thấy lệnh
scheme-r4rs: komanda nerasta
scheme-r4rs: Kommando nicht gefunden.
scheme-r4rs: kommandot finns inte
scheme-r4rs: komut yok
scheme-r4rs: nie znaleziono polecenia
scheme-r4rs: níor aimsíodh an t-ordú
scheme-r4rs: no se encontró la orden
scheme-r4rs: no s'ha trobat l'ordre
scheme-r4rs: opdracht niet gevonden
scheme-r4rs: parancs nem található
scheme-r4rs: perintah tidak ditemukan
scheme-r4rs: príkaz nenájdený
scheme-r4rs: příkaz nenalezen
scheme-r4rs: команда не найдена
scheme-r4rs: командата не е открита
scheme-r4rs: 命令找不到
scheme-r4rs: コマンドが見つかりません