Comments on: SICP sections 3.1.2 – 3.1.3

By: charles

charles — Sat, 09 Jan 2010 15:46:05 +0000

the procedure rand-update isn’t imaginary. If you go to the SICP website, you can download support code for the chapters. ch3support.scm contains the definition of rand-update.

By: flybirding

flybirding — Thu, 09 Jul 2009 05:10:48 +0000

em,yes.
Previously I choosed the language->legacy language->R5RS in DrScheme 4.1.5 when I came across the problem.
Now I choose the language->legacy language->Pretty Big in DrScheme 4.1.5,then exercise 3.5 could run.
It is a problem of Scheme programming envionment.
Thanks:)

By: eliben

eliben — Thu, 09 Jul 2009 03:42:38 +0000

@flybirding,

The only imported function that is required to run this code is ’square’, which I’ve defined eariler:

(define (square x)
  (* x x))

The real problem is that PLT have changed their language considerably in version 4. My code should execute with versions 3+, or in some kind of compatibility mode.

By: flybirding

flybirding — Wed, 08 Jul 2009 15:55:25 +0000

Exercise 3.5
hi,i copy your PLT Scheme code in my DrScheme to see the results,but i get the error”reference to undefined identifier: printf” etc.
I think there must be something to import.
Could you show wholly the source code for Exercise 3.5.
Thank you very much:)

By: eliben

eliben — Thu, 28 Aug 2008 16:02:19 +0000

I guess that if one reads the small print of the contract, you’re right. But I think my solution is good enough, as it provides the required protection, and does so in a much more elegant manner than the solution to the original requirement leads to.

By: Jason

Jason — Mon, 25 Aug 2008 22:56:39 +0000

I think you are missing an requirement here for Exercise 3.7: “Define a procedure make-joint that accomplishes this. Make-joint should take three arguments. The first is a password-protected account. The second argument must match the password with which the account was defined in order for the make-joint operation to proceed.”

The questions asks to signal an indication that the make-joint was not successful due to an incorrect acc-pass, yours only fail when the joint account try to withdraw money.