That book is amazing. Enjoy working through it, it will stretch your mind.
However, keep in mind that their emphasis is on getting a feel for how
recursion works. Real world Clojure code (any Lisp really) de-emphasizes
recursion to some extent. Particularly with regard to list (sequence)
processing (the name Lisp comes from "List processing" after all), Clojure has
a powerful library of functions that handle much of what the book implements
recursively. For example, if you would like to apply a function f to each
element in a list you could write code similar to the book:
(defn my-map [f l]
(cond (empty? l) '()
:else (cons (f (first l)) (my-map f (rest l)))) )
(my-map inc '(1 2 3 4 5)) => (2 3 4 5 6)
Here we apply the "First Commandment"--is the list l empty? If so, return an
empty list. Otherwise, apply the function to the first element of the list and
recursively process the rest of the list.
We could accomplish the same thing more succinctly in Clojure like this:
(map inc '(1 2 3 4 5)) => (2 3 4 5 6)
Clojure has a built-in 'map' function which iterates over each element in a
sequence, not merely lists:
(map dec [2 4 6 8]) => (1 3 5 7)
(map #(Character/toUpperCase %) "Is this not pung?") => (\I \S \space \T \H \I
\S \space \N \O \T \space \P \U \N \G \?)
Furthermore, the book is pretty much using a dialect of Lisp called Scheme, and
the semantics are a little different from Clojure. For instance, Clojure does
not have the concept of 'atom'.
It may actually be easier to work through the book in a Scheme environment (I
used Common Lisp though). But what you learn there will help you later with
Clojure.
In fact, if you are brave here is some of the material from chapter 9 dealing
with the Y-Combinator implemented in Clojure. It's pretty weird:
http://groups.google.com/group/clojure/browse_thread/thread/c9bd4e79e5877a66
Have all good days,
David Sletten
On Sep 21, 2010, at 6:38 PM, ax2groin wrote:
> Newbie here, to both LISP and Clojure. A friend has lent me a copy of
> "The Little LISPer" and I've started working through it, using some
> web resources to translate it into clojure.
>
> My questions: How relevant are the ten commandments? What modification
> need to be made ... either to the commandments or to your code in
> clojure?
>
> I ask because the first commandment (always ask null?) hasn't
> translated directly into any single statement for me. I can achieve
> the same with (or) to navigate the difference between nil and () in
> clojure, but sure that difference is in there for a reason.
>
> Any other input on the other commandments or using the book in
> general?
>
> Thanx
>
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