In DrRacket I can simply set #lang basic-demo-3, then in REPL say
> let x = 5
> print x
5
In command line I tried
racket -I basic-demo-3
but it doesn't work.
$ racket -I basic-demo-3
Welcome to Racket v8.7 [cs].
> let x = 5
; let: undefined;
; cannot reference an identifier before its definition
; in module: top-level
; [,bt for context]
> ; x: undefined;
; cannot reference an identifier before its definition
; in module: top-level
; [,bt for context]
> ; =: undefined;
; cannot reference an identifier before its definition
; in module: top-level
; [,bt for context]
> 5
>