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
   

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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
   

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3. View Slide

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5. The entire language can be
   built with quote, if, lambda, set!
   + variables, constants and procedure calls
   

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6. It’s a symbolic, homoiconic
   language with strong
   metaprogramming features.
   

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7. One standard, many
   implementations.
   

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8. More than 70 implementations
   targeting native code, JVM, CLR,
   JS, micro-CPUs, etc.
   

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9. ABSTRACT SYNTAX TREES
   

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10. public static int fact(int n)
    {
    if ( n == 0 )
    return 1;
    else
    return n*fact(n-1);
    }
    

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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);
    }
    

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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))))
    

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13. Parse AST Codegen
    (if (equal? n
    1
    (* n
    (fact
    (- n 1))))
    0)
    

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14. Parse AST Codegen
    (if (equal? n
    1
    (* n
    (fact
    (- n 1))))
    0)
    

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15. PROPER TAIL RECURSION
    

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16. (if (zero? n) 1
    (* n (fact (- n 1))))
    

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17. (define (fact n)
    (if (zero? n) 1
    (* n (fact (- n 1)))))
    

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18. (define (fact n)
    (if (zero? n) 1
    (* n (fact (- n 1)))))
    

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19. (define (fact n)
    (if (zero? n) 1
    (* n (fact (- n 1)))))
    if
    ==
    n 0
    1
    n
    *
    fact
    -
    1
    n
    

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20. (define (fact n)
    (if (zero? n) 1
    (* n (fact (- n 1)))))
    if
    ==
    n 0
    1
    n
    *
    fact
    -
    1
    n
    

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21. (define (fact n)
    (if (zero? n) 1
    (* n (fact (- n 1)))))
    if
    ==
    n 0
    1
    n
    *
    fact
    -
    1
    n
    

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22. n
    *
    fact
    -
    1
    n
    

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23. n
    *
    fact
    -
    1
    n
    

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24. -
    1
    n
    fact
    n
    *
    NON-TAIL RECURSIVE
    

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25. -
    1
    n
    fact
    n
    *
    acc
    TAIL RECURSIVE
    

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26. -
    1
    n
    fact
    n
    *
    acc
    TAIL RECURSIVE
    (define (fact n acc)
    (if (zero? n) acc
    (fact (- n 1)
    (* n acc))))
    

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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))))
    

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28. QUOTATION
    

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29. (quote (+ 1 2)) > (+ 1 2)
    ‘(+ 1 2)) > (+ 1 2)
    

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30. (quasiquote (* 2 ,(+ 1 2))) > ‘(* 2 3)
    `(* 2 ,(+ 1 2))) > ´(* 2 3)
    

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31. HOMOICONICITY
    

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32. Code is Data
    Data is Code
    

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33. (define code
    ‘(let ((age 36))
    (* age 365)))
    (print code) > ‘’(define ...)’’
    (eval code) > 13140
    

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34. (assert-equal
    (* 36 365)
    1314)
    «Error:
    (* 36 365) returned 13140,
    which is not equal to 1314»
    

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35. (asm
    (mov ax 1)
    (int #x10))
    

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36. (select
    (age name)
    (from store))
    

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37. (html
    (head (title «Foo»))
    (body
    (h1 «Bar»)
    (p (= color red)
    «Welcome»)))
    

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38. (json
    (first-name «John»)
    (last-name «Smith»)
    (age 25))
    

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39. CLOSURES
    

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40. closure = code + environment
    

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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)))
    

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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)))
    

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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))
    

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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))
    

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45. MACROS
    

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46. A macro is a compile-time
    change in the AST.
    It is used to control
    evaluation.
    

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47. (defmacro (when test do-stuff)
    `(if ,test ,do-stuff))
    (when #false (format-disk))
    

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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 ...)))))
    

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49. CONTINUATIONS
    

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50. continuation = reified call-stack
    

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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))))
    

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52. (print
    (* 10 12))
    

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53. (print
    (* 10 (call/cc
    (lambda (c)
    12))))
    (print
    (* 10 (call/cc
    (lambda (c)
    12))))
    

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54. (print
    (* 10 (call/cc
    (lambda (c)
    12))))
    

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55. (print
    (* 10 (call/cc
    (lambda (c)
    12))))
    print |
    * | 10 | ?
    Continuation
    

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56. print |
    * | 10 | ?
    Continuation
    (lambda (val)
    (print (* 10 val))
    

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57. (define redo #f) ; initialize
    (print «Result: »
    (* 10 (call/cc
    (lambda (cont)
    (set! redo cont)
    0))))
    (redo 10)
    (redo 12)
    

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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)
    

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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
    

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60. DEMO TIME
    

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