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Using eval in Scheme

Started by TheUnbeliever Feb 13, 2007 at 1:41 PM 1 replies 1.3k views

Original Post

104

Feb 13, 2007 at 1:41 PM

I'm working through SICP at the moment, but in a brief diversion looking for something entirely separate, I hit upon eval. My understanding is that, according to the Scheme standard, it should work something like: (eval '(+ 2 2) (scheme-report-environment 5)) or (eval '(+ 2 2) (null-environment 5)) However, typing this into the MIT Scheme interpreter tells me that both scheme-report-environment and null-environment are unbound variables. So, does anyone know what I've misunderstood or am missing?

TheUnbeliever

Author

104

TheUnbeliever

Feb 13, 2007 at 1:53 PM

Okay, I actually tried RTF-MIT-M, and discovered that it works with

(eval '(+ 2 2) (the-environment))

Which is fine by me, since according to the Scheme website only a few implementations actually stick to R5RS.

aviosity

Feb 13, 2007 at 3:31 PM

Hey TheUnbeliever,

Great to see someone else using Scheme!

You're correct in that few people are using the proper standard as it is. At my university (Indiana) we use Scheme almost exclusively, and we use Petite Chez Scheme (disclosure - the professor who wrote Chez Scheme is at Indiana). Every Scheme interpreter I've used, I've had to hunt through the documentation because I learned in Petite, but the variable names used are different in every interpreter. Caused a lot of confusion when I tried using Dr. Scheme :-P.

My advice for any Schemer is to RTM before using a new environment, even different versions of the same one, because the only constant I've found is that they're all different. Hope you're finding Scheme fun and rewarding!

Aviosity

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