Minor bugfixes and two new definitions #37
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Changed rename-in to only-in, as re-importing the rest of the Racket package would be redundant.
Modified set! so that if there's an amb expression active, backtracking will undo assignments. This is necessary to complete exercise 4.44.
Changed inc and dec to refer to the existing Racket functions add1 and sub1 rather than being redefined from scratch.
sicp/main.rkt
Outdated
| @@ -24,8 +25,8 @@ | |||
| (define+provide nil '()) | |||
| (define+provide the-empty-stream '()) | |||
| (define+provide stream-null? null?) | |||
| (define+provide (inc x) (+ x 1)) | |||
| (define+provide (dec x) (- x 1)) | |||
| (define+provide inc add1) | |||
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We intentionally do not do this because:
(define inc add1)
(println inc) ;=> #<procedure:add1>
prints a name that we do not want.
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I hadn't thought of that. I guess I can revert that part, then. What about the other changes?
This reverts commit 623ac59.
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Thanks for the PR! You said that:
Can I ask what issue did you encounter that make you think that this is a "bug"? I agree that I will have to take a look at the book to be sure if other changes look alright. Let me also ping @soegaard in case he sees anything. |
When you open main.rkt in DrRacket with the |
Fixed a bug in the require statement for racket:random and changed inc and dec to use built-in functions that did the same thing instead of being defined from scratch.
Added apply-in-underlying-scheme because the book's solution of just using the line (define apply-in-underlying-scheme apply) at the start of the metacircular evaluator isn't compatible with how Racket handles definitions.
Changed the way set! is handled so that Exercise 4.45 can be completed successfully. If there's an amb statement active, calls to set! will modify amb-fail so that backtracking will undo assignments. This only kicks in if the amb tree isn't currently empty, so it should have no discernible performance impact on programs that don't use amb operations.
Added the user-initial-environment primitive so that the code for the query system in Section 4.4.4 can be run as-is.