Possible errata page 129, exercise 4.29

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Jul 17, 2013, 12:57:16 PM7/17/13
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I'm working my way through the book, and when entering this code from pg 129 ex 4.29
(run "
let a = newarray(2, -99)
    p = proc (x)
         let v = arrayref(x,1)
         in arrayset(x,1,-(v, -1))
in begin
     arrayset(a, 1, 0);
     (p, a);
     (p, a);
I get  " parsing: at line 3: looking for "in", found identifier p in production..."  
I'm keying all my code incrementally as I work through the exercises so this could just be my bug, but when I look in the  code for mutable pairs or the site, I see nothing which would suggest let should allow multiple declarations in a let.  Is this really a typo?

Mitchell Wand

Jul 17, 2013, 4:16:37 PM7/17/13
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Yup, if you look at the grammar for MUTABLE-PAIRS, you'll see that it only allows a single declaration in a let.

This probably wasn't intentional, but it's in an exercise.  You are being asked to modify the language, so do it.  ;)


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Jul 18, 2013, 12:21:30 PM7/18/13
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Thanks .  I didn't think it was intentional but sure  why not...
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