Print Page - List algorithm in interactive tutorial gives error

Title: List algorithm in interactive tutorial gives error
Post by: bluenote on November 28, 2014, 05:50:09 PM

Hi There,

The generic list algorithm in the interactive tutorial (//http)produces an error when I try to evaluate it.

I was able to fix up the code and get it working (provided below) as per the spirit of the tutorial. Perhaps that tutorial is out of date to newer language features or something.

Old non-working code

Code Select Expand
(define (list-length a-list)
(if (first a-list)
  (+ 1 (list-length (rest a-list)))
  0))

My modified version which seems to work

Code Select Expand
(define (list-length a-list)
(if a-list
  (+ 1 (list-length (rest a-list)))
  0))

Title: Re: List algorithm in interactive tutorial gives error
Post by: Lutz on November 29, 2014, 06:35:33 AM

Thanks for the correction - now online (//http). The change should have been made in 2008 when the empty list would would now be taken as Boolean false by if and first on an empty list returned now an error.

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Forum => Anything else we might add? => Topic started by: bluenote on November 28, 2014, 05:50:09 PM