R⁷RS Scheme

An introduction to the Scheme programming language. Topics include abstract syntax trees (ASTs), proper tail recursion, quotation, homoiconicity, closures, macros and continuations.

After going through the slides, we went through some example Scheme programs. We spent some time looking at how we could implement things like exception handling, object orientation, non-deterministic programming and so on using Scheme primitives.

Link to MeetUp:
http://www.meetup.com/Functional-escape/events/126170252/

Link to Mickey Scheme:
https://github.com/cslarsen/mickey-scheme

Transcript

1. R7RS SCHEME C hr i st i an S t i gen Larsen 2013 - 08 - 29
2. «Programming languages should be designed not by piling feature on top of feature, but by removing the weaknesses and restrictions that make additional features appear necessary.»
   From the SC HEME standards
5. The entire language can be built with quote, if, lambda, set!
   + variables, constants and procedure calls
   
6. It’s a symbolic, homoiconic language with strong metaprogramming features.
   
7. One standard, many implementations.
   
8. More than 70 implementations targeting native code, JVM, CLR, JS, micro-CPUs, etc.
   
9. ABSTRACT SYNTAX TREES
10. public static int fact(int n)
    {
    if ( n == 0 )
    return 1;
    else
    return n*fact(n-1);
    }
11. if == n 0 1 n * fact - 1 n public static int fact(int n)
    {
    if ( n == 0 )
    return 1;
    else
    return n*fact(n-1);
    }
12. if == n 0 1 n * fact - 1 n public static int fact(int n)
    {
    if ( n == 0 )
    return 1;
    else
    return n*fact(n-1);
    } (if (equal? n 0) 1 (* n (fact (- n 1))))
13. Parse AST Codegen (if (equal? n 1 (* n (fact (- n 1)))) 0)
14. Parse AST Codegen (if (equal? n 1 (* n (fact (- n 1)))) 0)
15. PROPER TAIL RECURSION
16. (if (zero? n) 1 (* n (fact (- n 1))))
17. (define (fact n) (if (zero? n) 1 (* n (fact (- n 1)))))
18. (define (fact n) (if (zero? n) 1 (* n (fact (- n 1)))))
19. (define (fact n) (if (zero? n) 1 (* n (fact (- n 1))))) if == n 0 1 n * fact - 1 n
20. (define (fact n) (if (zero? n) 1 (* n (fact (- n 1))))) if == n 0 1 n * fact - 1 n
21. (define (fact n) (if (zero? n) 1 (* n (fact (- n 1))))) if == n 0 1 n * fact - 1 n
22. n * fact - 1 n
23. n * fact - 1 n
24. - 1 n fact n * NON-TAIL RECURSIVE
    
25. - 1 n fact n * acc TAIL RECURSIVE
    
26. - 1 n fact n * acc TAIL RECURSIVE
    (define (fact n acc) (if (zero? n) acc (fact (- n 1) (* n acc))))
27. - 1 n fact n * acc TAIL RECURSIVE
    (define (fact n acc) (if (zero? n) acc (fact (- n 1) (* n acc)))) (define (fact n acc) (if (zero? n) acc (fact (- n 1) (* n acc))))
28. QUOTATION
29. (quote (+ 1 2)) > (+ 1 2) ‘(+ 1 2)) > (+ 1 2)
30. (quasiquote (* 2 ,(+ 1 2))) > ‘(* 2 3) `(* 2 ,(+ 1 2))) > ´(* 2 3)
31. HOMOICONICITY
32. Code is Data Data is Code
33. (define code ‘(let ((age 36)) (* age 365))) (print code) > ‘’(define ...)’’ (eval code) > 13140
34. (assert-equal (* 36 365) 1314) «Error: (* 36 365) returned 13140, which is not equal to 1314»
35. (asm (mov ax 1) (int #x10))
36. (select (age name) (from store))
37. (html (head (title «Foo»)) (body (h1 «Bar») (p (= color red) «Welcome»)))
38. (json (first-name «John») (last-name «Smith») (age 25))
39. CLOSURES
40. closure = code + environment
41. (let ((name ‘‘foo’’)) (lambda (title) (print title name))) (let ((name ‘‘foo’’)) (lambda (title) (print title name))) (let ((name ‘‘foo’’)) (lambda (title) (print title name)))
42. (let ((name ‘‘foo’’)) (lambda (title) (print title name))) (let ((name ‘‘foo’’)) (lambda (title) (print title name))) (let ((name ‘‘foo’’)) (lambda (title) (print title name)))
43. (define send #f) ; initialize (define recv #f) (let ((secret-message ‘‘none’’)) (set! send (lambda (str) (set! secret-message str))) (set! recv (lambda () secret-message))) (send ‘‘Meet me by the docks at midnight’’) (print (recv))
44. (define send #f) ; initialize (define recv #f) (let ((secret-message ‘‘none’’)) (set! send (lambda (str) (set! secret-message str))) (set! recv (lambda () secret-message))) (send ‘‘Meet me by the docks at midnight’’) (print (recv))
45. MACROS
46. A macro is a compile-time change in the AST. It is used to control evaluation.
47. (defmacro (when test do-stuff) `(if ,test ,do-stuff)) (when #false (format-disk))
48. (define-syntax when (syntax-rules () ((when test code ...) (if test (begin code ...))))) (define-syntax when (syntax-rules () ((when test code ...) (if test (begin code ...))))) (define-syntax when (syntax-rules () ((when test code ...) (if test (begin code ...))))) (define-syntax when (syntax-rules () ((when test code ...) (if test (begin code ...))))) (define-syntax when (syntax-rules () ((when test code ...) (if test (begin code ...))))) (define-syntax when (syntax-rules () ((when test code ...) (if test (begin code ...)))))
49. CONTINUATIONS
50. continuation = reified call-stack
51. (print (* 10 (call/cc (lambda (c) 12)))) (print (* 10 (call/cc (lambda (c) 12)))) (print (* 10 (call/cc (lambda (c) 12)))) (print (* 10 (call/cc (lambda (c) 12))))
52. (print (* 10 12))
53. (print (* 10 (call/cc (lambda (c) 12)))) (print (* 10 (call/cc (lambda (c) 12))))
54. (print (* 10 (call/cc (lambda (c) 12))))
55. (print (* 10 (call/cc (lambda (c) 12)))) print | * | 10 | ? Continuation
56. print | * | 10 | ? Continuation (lambda (val) (print (* 10 val))
57. (define redo #f) ; initialize (print «Result: » (* 10 (call/cc (lambda (cont) (set! redo cont) 0)))) (redo 10) (redo 12)
58. (define redo #f) ; initialize (print «Result: » (* 10 (call/cc (lambda (cont) (set! redo cont) 0)))) (redo 10) (redo 12) (define redo #f) ; initialize (print «Result: » (* 10 (call/cc (lambda (cont) (set! redo cont) 0)))) (redo 10) (redo 12)
59. (define redo #f) ; initialize (print «Result: » (* 10 (call/cc (lambda (cont) (set! redo cont) 0)))) (redo 10) (redo 12) (define redo #f) ; initialize (print «Result: » (* 10 (call/cc (lambda (cont) (set! redo cont) 0)))) (redo 10) (redo 12) (define redo #f) ; initialize (print «Result: » (* 10 (call/cc redo-val (lambda (cont) (set! redo cont) 0)))) (redo 10) ; redo-val (redo 12) ; redo-val
60. DEMO TIME