[racket] world/universe update model (functional update redux), using the I/O monad for state

On Dec 12, 2011, at 7:55 PM, Matthias Felleisen wrote:

> 
> Is the below really much less natural to write? I really enjoyed playing the qwerty row from left to right, or perhaps I was pressing the number keys at the same time :-)

You're cheating! Unless quasiquote is a new part of htdp/2e....

And actually: yes, I think that the below still is less natural to write. Student says: why do we have to write down the parts that don't change? Doesn't the redundancy introduce extra opportunities for error?

John



> 
> #lang racket
> 
> (require (except-in (planet clements/rsound)
>                    overlay
>                    scale)
>         2htdp/universe
>         2htdp/image)
> 
> (define octave 48)
> (define volume .4)
> (define duration 22050)
> 
> (define (main)
>  (big-bang `(,octave ,volume ,duration)
>            (to-draw my-draw)
>            (on-key  my-key)))
> 
> (define (my-draw num)
>  (place-image/align (text (format "~s" num) 11 'red) 10 50 'left 'top (empty-scene 100 100)))
> 
> (define (my-key w key)
>  (match (cons key w)
>    [`("0" ,oct ,vol ,dur) `( 0 ,vol ,dur)]
>    [`("1" ,oct ,vol ,dur) `(12 ,vol ,dur)]
>    [`("2" ,oct ,vol ,dur) `(24 ,vol ,dur)]
>    [`("3" ,oct ,vol ,dur) `(36 ,vol ,dur)]
>    [`("4" ,oct ,vol ,dur) `(48 ,vol ,dur)]
>    [`("5" ,oct ,vol ,dur) `(60 ,vol ,dur)]
>    [`("6" ,oct ,vol ,dur) `(72 ,vol ,dur)]
>    [`("7" ,oct ,vol ,dur) `(84 ,vol ,dur)]
>    [`("8" ,oct ,vol ,dur) `(96 ,vol ,dur)]
>    [`((or "=" "+") ,oct ,vol ,dur) `(,oct ,(if (< vol 1) (+ vol .1) vol) ,dur)]
>    [`((or "-" "_") ,oct ,vol ,dur) `(,oct ,(if (> vol 0) (- vol .1) vol) ,dur)]
>    [`("z" ,oct ,vol ,dur) `(,oct ,vol ,(if (> dur 11025) (- dur 11025) dur))]
>    [`("x" ,oct ,vol ,dur) `(,oct ,vol ,(if (< dur 88200) (+ dur 11025) dur))]
>    [`("q" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 12 oct)) vol dur)) w]
>    [`("w" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 13 oct)) vol dur)) w]
>    [`("e" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 14 oct)) vol dur)) w]
>    [`("r" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 15 oct)) vol dur)) w]
>    [`("t" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 16 oct)) vol dur)) w]
>    [`("y" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 17 oct)) vol dur)) w]
>    [`("u" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 18 oct)) vol dur)) w]
>    [`("i" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 19 oct)) vol dur)) w]
>    [`("o" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 20 oct)) vol dur)) w]
>    [`("p" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 21 oct)) vol dur)) w]
>    [`("[" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 22 oct)) vol dur)) w]
>    [`("]" ,oct ,vol ,dur) (play (make-tone (midi-note-num->pitch (+ 23 oct)) vol dur)) w]
>    [`("a" ,oct ,vol ,dur) (play c-hi-hat-1) w]
>    [`("s" ,oct ,vol ,dur) (play c-hi-hat-2) w]
>    [`("d" ,oct ,vol ,dur) (play o-hi-hat) w]
>    [`("f" ,oct ,vol ,dur) (play snare) w]
>    [`("g" ,oct ,vol ,dur) (play bassdrum) w]
>    [`("h" ,oct ,vol ,dur) (play bassdrum) w]
>    [`("j" ,oct ,vol ,dur) (play bassdrum-synth) w]         
>    [`("k" ,oct ,vol ,dur) (play clap-1) w]
>    [`("l" ,oct ,vol ,dur) (play clap-2) w]
>    [`(";" ,oct ,vol ,dur) (play crash-cymbal) w]
>    [else w]
>    [else (displayln `(no match ,w))]))
> 
> (main)

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