> 2
2
> "abc"
"abc"
> +
#<procedure:+>
> a
[image] [image] a: undefined;
 cannot reference an identifier before its definition
> (define a 5)
> a
5
> (+ 2 a)
7
> (1 2 3)
[image] [image] application: not a procedure;
 expected a procedure that can be applied to arguments
  given: 1
> (2 + a)
[image] [image] application: not a procedure;
 expected a procedure that can be applied to arguments
  given: 2
> (+ -)
[image] [image] +: contract violation
  expected: number?
  given: #<procedure:->
> (- 5)
-5
> (+ 5)
5
> (+)
0
> (*)
1
> (- 5)
-5
> -5
-5
> (+ -4 -2)
-6
> (define b +)
> b
#<procedure:+>
> (b 2 5)
7
> (define + -)
> (+ 4 5)
-1
> (b 4 5)
9
> (define + b)
> +
#<procedure:+>
> (+ 2 3)
5
> (quote (+ 2 3))
(+ 2 3)
> x
[image] [image] x: undefined;
 cannot reference an identifier before its definition
> a
5
> (define c (+ a c))
[image] [image] c: undefined;
 cannot reference an identifier before its definition
> (define c '(+ a c))
> c
(+ a c)
> (define (square x) (* x x))
> square
#<procedure:square>
> (square 5)
25
> (square (square 2))
16