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Thanks for the tip, but when I tried to run it under mzscheme I got the error: map: all lists must have same size; arguments were: #<procedure:+> () (1). Also c

Thanks for the tip, but when I tried to run it under mzscheme I got the error: map: all lists must have same size; arguments were: #<procedure:+> () (1). Also could you explain why set! and list-ref are bad?

vtail 15y ago
You are doing yourself a great service by learning Scheme - that can fundamentally change how you think about programming. Reading the first chapter of SICP[0] will change you forever. Yet right now you're using Scheme as a Python/C/Ruby with a strange syntax, while it's a totally different language with its own idioms. You should learn them to master Scheme. As for your particular questions: 1. map yields an error under mzscheme I'm at work, and didn't have access to a proper scheme, so I used an online REPL[1], which apparently is more forgiving. Regardless, you can write your own map (a good exercise!) that stops as soon as one of the arguments is exhausted. Make it tail-recursive[2] as well! 2. list-ref is bad Lists are beautiful data structures designed for recursive algorithms. If you are using lists and not using recursion (or a hidden recursion in the form of map), you're doing something wrong. list-ref uses list as a vector, which has a performance implications - your algorithm is O(n^3) while mine is O(n^2). 3. set! is bad Margins are too small for a proper explanation :), but basically set! has side-effects[3], and functional programming should avoid having them. Have fun learning Scheme! [0] http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-9.html#%_chap_1 http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-9.html#... [1] http://www.bluishcoder.co.nz/jsscheme/ http://www.bluishcoder.co.nz/jsscheme/ [2] http://en.wikipedia.org/wiki/Tail_call http://en.wikipedia.org/wiki/Tail_call [3] http://en.wikipedia.org/wiki/Side_effect_(computer_science) http://en.wikipedia.org/wiki/Side_effect_(computer_science)
- kunqiana 15y ago
  Just out of curiosity did you learn scheme primarily through books? Do you actually use the language on a daily basis? Maybe you are a lisp hacker?

vtail 15y ago

You are doing yourself a great service by learning Scheme - that can fundamentally change how you think about programming. Reading the first chapter of SICP[0] will change you forever. Yet right now you're using Scheme as a Python/C/Ruby with a strange syntax, while it's a totally different language with its own idioms. You should learn them to master Scheme. As for your particular questions: 1. map yields an error under mzscheme I'm at work, and didn't have access to a proper scheme, so I used an online REPL[1], which apparently is more forgiving. Regardless, you can write your own map (a good exercise!) that stops as soon as one of the arguments is exhausted. Make it tail-recursive[2] as well! 2. list-ref is bad Lists are beautiful data structures designed for recursive algorithms. If you are using lists and not using recursion (or a hidden recursion in the form of map), you're doing something wrong. list-ref uses list as a vector, which has a performance implications - your algorithm is O(n^3) while mine is O(n^2). 3. set! is bad Margins are too small for a proper explanation :), but basically set! has side-effects[3], and functional programming should avoid having them. Have fun learning Scheme! [0] http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-9.html#%_chap_1 http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-9.html#... [1] http://www.bluishcoder.co.nz/jsscheme/ http://www.bluishcoder.co.nz/jsscheme/ [2] http://en.wikipedia.org/wiki/Tail_call http://en.wikipedia.org/wiki/Tail_call [3] http://en.wikipedia.org/wiki/Side_effect_(computer_science) http://en.wikipedia.org/wiki/Side_effect_(computer_science)

kunqiana 15y ago
Just out of curiosity did you learn scheme primarily through books? Do you actually use the language on a daily basis? Maybe you are a lisp hacker?