lazy (prime?/fast)

[Scott Heidbrink]

I don't understand (prime?/fast n) so it tests if n is prime "but tests only prime factors from primes/fast," but primes/fast is all primes constructed with prime?/fast......I'm having trouble visualizing how this would work, can you explain it a different way or show me an example?

[Jay McCarthy]

I gave you many examples in class. nats was based on nats and fibs was
based on fibs. Like that.

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--
Jay McCarthy <j...@cs.byu.edu>
Assistant Professor / Brigham Young University
http://faculty.cs.byu.edu/~jay

"The glory of God is Intelligence" - D&C 93

[Scott Heidbrink]

But those both started with a base case and from the way i understand this is neither of these has a base case?

On Thursday, December 5, 2013 3:39:35 PM UTC-7, Jay McCarthy wrote:

I gave you many examples in class. nats was based on nats and fibs was
based on fibs. Like that.

On Thu, Dec 5, 2013 at 3:31 PM, Scott Heidbrink
<scott.h...@gmail.com> wrote:
> I don't understand (prime?/fast n) so it tests if n is prime "but tests only
> prime factors from primes/fast," but primes/fast is all primes constructed
> with prime?/fast......I'm having trouble visualizing how this would work,
> can you explain it a different way or show me an example?
>
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[Dan Burton]

(prime?/fast n) so it tests if n is prime "but tests only prime factors from primes/fast," but primes/fast is all primes constructed with prime?/fast

The base case is the first prime number: 2. Once you've bootstrapped the computation by hardcoding 2 as the first prime number, then the mutual recursion should work just fine. Where you put the base case is up to you.

[Jay McCarthy]

Yup, Dan's right, there's nothing special about the base cases that we
used for nats and fibs. You just need to pick something.

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[Ben Draut]

How do we avoid cyclic dependency issues in Racket when doing mutual recursion like this?

When both prime?/fast and primes/fast call each other, Racket tells me that I can't use one of them before it's definition. (Whichever is defined second)

[Jay McCarthy]

On Mon, Dec 9, 2013 at 8:20 AM, Ben Draut <dra...@gmail.com> wrote:
> How do we avoid cyclic dependency issues in Racket when doing mutual
> recursion like this?
>
> When both prime?/fast and primes/fast call each other, Racket tells me that
> I can't use one of them before it's definition. (Whichever is defined
> second)

Put the test for both after each. For example

CODE 1
TEST 1
CODE 2
TEST 2

is what you'd normally do, but you should do

CODE 1
CODE 2
TEST 1
TEST 2