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Merge pull request #205 from cmsc430/fall-2025
Fall 2025
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‎www/assignments/6.scrbl‎

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#lang scribble/manual
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@(require "../defns.rkt")
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@title[#:tag "Assignment 6" #:style 'unnumbered]{Assignment 6: List primitives and n-ary primitives}
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@(require "../defns.rkt"
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"../notes/ev.rkt")
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@title[#:tag "Assignment 6" #:style 'unnumbered]{Assignment 6: List and vector primitives}
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@(require (for-label a86 (except-in racket ...)))
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@(require racket/port)
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@bold{Due: @assign-deadline[6]}
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Details of this assignment will be released later in the semester.
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@;{ All this to silence some Makefile output on Linux -- should probably be taken care of at the Makefile level }
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@(ev '(begin (define p (current-output-port))
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(current-output-port (open-output-string))
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(require hoax-plus)
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(current-output-port p)))
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The goal of this assignment is to gain proficiency with our
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representation of memory-allocated values by implementing a number of
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list and vector primitives.
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@section[#:tag-prefix "a6-" #:style 'unnumbered]{Overview}
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For this assignment, you are given a @tt{hoax-plus.zip} file on ELMS
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with a starter compiler similar to the @seclink["Hoax"]{Hoax}
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language we studied in class.
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@section[#:tag-prefix "a6-" #:style 'unnumbered]{Hoax+}
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The Hoax+ language extends the Hoax language we studied in class with four
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new unary primitives:
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@itemlist[
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@item{@racket[length]: given a list, computes its length.}
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@item{@racket[reverse]: given a list, computes a list with elements in the reverse order of the given list.}
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@item{@racket[list->vector]: given a list, computes a vector with elements in the order of the given list.}
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@item{@racket[vector->list]: given a vector, computes a list with elements in the order of the given vector.}
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]
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Unlike past assignments, you do not need to bring forward in any
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features from earlier assignments.
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@section[#:tag-prefix "a6-" #:style 'unnumbered]{List and vector primitves}
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The new primitives have been added to the parser and the interpreter.
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The behavior of compiled primitives should be consistent with the
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interpreter:
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@ex[
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(interp (parse '(length '())))
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(interp (parse '(length (cons 1 (cons 2 '())))))
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(interp (parse '(length #f)))
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(interp (parse '(reverse '())))
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(interp (parse '(reverse (cons 1 (cons 2 '())))))
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(interp (parse '(reverse #f)))
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(interp (parse '(list->vector '())))
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(interp (parse '(list->vector (cons 1 (cons 2 '())))))
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(interp (parse '(list->vector #f)))
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(interp (parse '(vector->list (make-vector 0 #t))))
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(interp (parse '(vector->list (make-vector 2 #t))))
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(interp (parse '(vector->list #f)))
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]
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The interpreter is consistent with Racket's own behavior, so if you're
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unsure about what your compiler should do, you can look to Racket (or
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the interpreter) for guidance:
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@ex[
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(length '())
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(length (cons 1 (cons 2 '())))
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(eval:error (length #f))
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(reverse '())
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(reverse (cons 1 (cons 2 '())))
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(eval:error (reverse #f))
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(list->vector '())
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(list->vector (cons 1 (cons 2 '())))
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(eval:error (list->vector #f))
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(vector->list (make-vector 0 #t))
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(vector->list (make-vector 2 #t))
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(eval:error (vector->list #f))
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]
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@subsection[#:tag-prefix "a6-" #:style 'unnumbered]{Testing}
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A small number of test cases have been provided in
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@tt{test/test-runner.rkt}. There is function called @racket[test]
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that contains I/O-free test cases and another called @racket[test/io]
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that contains I/O tests. To run these tests, @tt{raco test
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test/interp.rkt} will test the interpreter and @tt{raco test
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test/compile.rkt} will test the compiler. You are encouraged to add
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your own tests.
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@section[#:tag-prefix "a6-" #:style 'unnumbered]{Submitting}
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To submit, use @tt{make} from within the @tt{hoax-plus} directory to
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create a zip file containing your work and submit it to Gradescope.

‎www/defns.rkt‎

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"Thursday, September 25, 11:59PM"
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"Thursday, October 2, 11:59PM"
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"Thursday, October 23, 11:59PM"
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"Thursday, October 30, 11:59PM"
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"Thursday, November 6, 11:59PM"
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"Tuesday, November 4, 11:59PM"
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"Tuesday, November 11, 11:59PM"
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"Thursday, November 20, 11:59PM"
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"Thursday, December 4, 11:59PM")
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(sub1 i)))

‎www/notes/diagrams.rkt‎

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(define n 40)
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(define (make-str-cells s)
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(hc-append
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(foldl (λ (c p)
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(hc-append p
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(cc-superimpose (rectangle (/ n 2) n) ((current-code-tt) (string c)))))
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(cc-superimpose (rectangle n n) (code #,(string-length s)))
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(string->list s))
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(if (even? (string-length s))
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(rectangle 0 n)
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(cc-superimpose (rectangle (/ n 2) n) (code 0)))))
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(define (make-imm-cell i)
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(cc-superimpose
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(code #,i)
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(cb-superimpose (rectangle n n)
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(code cons)))
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(define (make-str-cell)
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(cb-superimpose (rectangle n n)
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(code str)))
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(define (make-box-cell)
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(cb-superimpose (rectangle n n)
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[`(cons ,_) (make-cons-cell)]
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[`(box ,_) (make-box-cell)]
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[`(vect ,_) (make-vect-cell)]
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[`(str ,_) (make-str-cell)]
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[(? string?) (make-str-cells v)]
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[_ (make-imm-cell v)]))
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(define (add-arrows spec cells p)
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;(printf "~a~n" spec)
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(match spec
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['() p]
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[(cons `(_ ,i) s)
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[(cons `(,_ ,(? integer? i)) s)
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(add-arrows s
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cells
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(fwd-pts-to (list-ref cells (sub1 (- (length cells) (length s))))
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heap)))
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(define heap/arrows/label
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(vc-append
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0
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heap/arrows
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(text "heap")))
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(vc-append 10
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(vc-append
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0
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heap/arrows
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(text "heap"))
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(text "← lower addresses, higher addresses →")))
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(define rax/label
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(vc-append 0 rax (text "rax")))
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(vc-append 10 (vc-append 0 rax (text "rax"))
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(text " ")))
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(inset
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(fwd-pts-to rax (list-ref heap i) (hc-append n rax/label heap/arrows/label))
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(* n 2))]))
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(fwd-pts-to rax (list-ref heap i)
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(hc-append n rax/label heap/arrows/label))
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0 (* n 2) 0 0)]))
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#;
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(define cons-quiz
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(list (make-heap-diagram
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'((cons 4)
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3
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'()
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2
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(cons 0)
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1
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(cons 2)))
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(make-heap-diagram
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'((cons 0)
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1
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(cons 2)
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2
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(cons 4)
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3
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'()))
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(make-heap-diagram
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'((cons 4)
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'()
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3
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(cons 0)
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2
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(cons 2)
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1))
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(make-heap-diagram
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'((cons 0)
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(cons 2)
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1
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(cons 4)
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2
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'()
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3))
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))
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;(text "← lower addresses, higher addresses →")
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#;
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(make-heap-diagram
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'((cons 0)

‎www/notes/hoax.scrbl‎

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(Pop rbx)
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(Ret))))
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This creates a string in memory like this:
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@make-heap-diagram['((str 0) "abc")]
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In this diagram, we use half-sized boxes to indicate that only 4 bytes
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are used per codepoint. Also the contents of the array are not
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values, but codepoints (shown as the letters the codepoint encodes).
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In odd length strings, we write @racket[0] for the padded element, but
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in reality there are arbitrary bits at that memory location, which is
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fine because they will never be read.
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At first glance, this looks remarkably similar to creating a vector,
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however there are some imporant things to notice:
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]
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Notice that a string like @racket["fred"] is not represented the same
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as a vector of characters @racket[#(#\f #\r #\e #\d)], which uses more
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space. Compare:
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@make-heap-diagram['((str 0) "fred")]
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versus:
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@make-heap-diagram['((vect 0) 4 #\f #\r #\e #\d)]
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Now let's set things up like we did before to be able to interactively
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write examples in order to arrive at the code for
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@racket[string-length], @racket[string-ref], and @racket[make-string]:

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