Welcome to DrRacket, version 8.7 [cs].
Language: racket, with debugging; memory limit: 128 MB.
> (+ 2 2)
4
> 2.3
2.3
> "hello"
"hello"
> +
#<procedure:+>
> a
. . a: undefined;
 cannot reference an identifier before its definition
> (define a 5)
> a
5
> (+ 2 3)
5
> (+ (- 5 8) (* 3 5))
12
> (1 2 3)
. . application: not a procedure;
 expected a procedure that can be applied to arguments
  given: 1
> (define b (+ b 2))
. . b: undefined;
 cannot reference an identifier before its definition
> (quote (1 2 3))
'(1 2 3)
> (1 2 3)
. . application: not a procedure;
 expected a procedure that can be applied to arguments
  given: 1
> ('+ 2 3)
. . application: not a procedure;
 expected a procedure that can be applied to arguments
  given: '+
> '+
'+
> (quote +)
'+
> +
#<procedure:+>
> (define a +)
> (a 2 3)
5
>