letrec exercise 3.32 and 3.33

[tim_sw]

Hello,

I've been trying to figure out how to add mutually recursive proc
definitions in letrec, extending it from the chapter 3 code downloaded
from the EPOL website.
My initial attempt was to add another type of expression to put inside
letrec, (which i called proc-defs)

(expression
("letrec"
proc-defs
"in" expression)
letrec-exp)

This triggered a cascade of changes all over the place, and it started
getting a little hacky, which felt wrong, so I was just wondering if I
am on the right path, and if anyone else has tried doing these
exercises before....
Thanks!
Tim

[Simina Branzei]

Hello Tim,

Yes I went through some of those exercises, and it does get quite hairy :-(. Also the debugging mechanism wasn't that good.  But  maybe it's just me not having enough experience with Scheme.

Simina

2008/11/24 tim_sw <tim_s...@yahoo.com>

[Dwayne Crooks]

For me it helped when I worked out the syntax and then the semantics

of mutually recursive letrec. Doing that provides a nice guide that helps

you to figure out the implementation. Furthermore, if you have trouble

figuring out the semantics then you should step through the semantics

of the program and reason out what needs to happen at each step.

i.e.

(value-of <<letrec even(x) ... odd(x) ... in (odd 13)>> p)

= (value-of <<(odd 13)>> ?)

How should the environment be extended so that it all works out. That's

the key thing you need to figure out. Play with some ideas and see how

you can continue the computation.

Hope that helps.

EOPL3 in Haskell (https://github.com/dwayne/eopl3)