On Mon, Dec 22, 2008 at 10:23 AM, Piotr 'Qertoip' Włodarek <qert...@gmail.com> wrote: > > Being new to Clojure, to Lisp and to functional programming in > general, I have some trouble wraping my head around it. > > As the first exercice, I would like to print multiplication table of > specified order, like: > (print-multiplication-table 3) > 1 2 3 > 2 4 6 > 3 6 9 > > I came that far: > > (defn multiplication-row [n k] > (map (partial * k) (range 1 (inc n)))) > > (defn multiplication-table [n] > (map (partial multiplication-row n) (range 1 (inc n)))) > > (println (multiplication-table 3)) ; => ((1 2 3) (2 4 6) (3 6 9)) > > Now, how to pretty print this? > > This does not work - prints nothing - why?: > (defn pretty-print-row [row] > (map print row))
The problem is that you are using map in two different ways here. In the multiplication-row and multiplication-table functions you are using it correctly as a function that applies a given function to all of the values in a collection, returning the results in a new collection. In the pretty-printing function you do not care about the results like you did in the above two functions, you care about the side-effects. For this, you can use doseq: 1:1 user=> (defn multiplication-row [n k] (map (partial * k) (range 1 (inc n)))) #'user/multiplication-row 1:3 user=> (defn multiplication-table [n] (map (partial multiplication-row n) (range 1 (inc n)))) #'user/multiplication-table 1:5 user=> (defn pretty-print-row [row] (doseq [v row] (print v \space)) (print \newline)) #'user/pretty-print-row 1:7 user=> (defn print-multiplication-table [n] (doseq [row (multiplication-table n)] (pretty-print-row row))) #'user/print-multiplication-table 1:9 user=> (print-multiplication-table 3) 1 2 3 2 4 6 3 6 9 nil 1:10 user=> (print-multiplication-table 5) 1 2 3 4 5 2 4 6 8 10 3 6 9 12 15 4 8 12 16 20 5 10 15 20 25 nil HTH, - J. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
