Programs as Data

The built-in Scheme ^2gccw8.md can represent ^bmog31.md, using Symbolic Programming.

> (list 'quotient 10 2)
(quotient 10 2)
> (eval (list 'quotient 10 2))
5

All the Scheme codes are just lists. We can write a program that writes a program.

A complex combination is a nested Pair like this:(A and B are another combination like (+ 3 2), etc.)

(define (fact n)
	(if (= n 0) 1 (* n (fact (- n 1)))))
 
(define (fact-exp n)
	(if (= n 0) 1 (list '* n (fact-exp (- n 1)))))

Generating Codes

Quasiquotation

There are two ways to quote an expression.

• Quote
• Quasiquote: Parts of a quasiquoted expression can be unquoted with comma

Example:

(define (sum-while initial-x condition add-to-total update-x)
    `(begin
        (define (f x total)
            (if ,condition
                (f ,update-x (+ total ,add-to-total))
            total))
    (f ,initial-x 0)))