On Dec 11, 11:14 am, ngocdaothanh <[email protected]> wrote:
> Because of indents, my previous Clojure code lied to my eyes that x,
> y, f, g are not at the same block level. This is my difficulty with
> Clojure. In short, I can't see a rough algorithm from any Clojure code
> any more just by seeing the shape (levels) of blocks. To understand a
> Clojure code, I have to look at every bit of code, look closer.
>
You should come up with a real code example instead of a bunch of (f
x) (y z) expressions... The example you show is not very idiomatic
clojure simply because it has side-effects. (Of course you need side-
effects, but they should be isolated).
If the code structure gets too complicated, simplify it by writing
functions or macros to better express your intent.
> > In Clojure we still need to look farther up the screen...
>
> Things in Erlang are immutable, so I think Clojure has no advantage
> over Erlang here.
>
> > Practice using comp & partial...
>
> What do you mean by "comp & partial"? Could you please explain?
comp is function composition, and partial is partial application. eg:
((comp negate inc) 6) -> -7
((partial + 1) 5) -> 6
using these to create new functions is called point-free style
I'm not so much a fan, and I don't think point-free style is
particularly idiomatic in Clojure (unlike in Haskell for example), but
it's sometimes less noisy than #() or fn expressions, so it's good to
know.
They're usually best used with filter and map.
>
> > (let [x 1
> > y (+ x 2)]
> > (f x)
> > (g y))
>
> Well, I know my example code can be rewritten like that, but I just
> could not give a better one.
I don't think there's any use for comp or partial in this case. it's
too simple.
>
> Rearranging like this reminds me of C, in which every variables must
> be listed beforehand. Since all Clojurians say "lazy" is good, I would
> say I prefer C++ because I can be lazy in it, I only have to declare a
> variable when I actually use it.
Your code examples are a bit pathological. Usually (hopefully), you
would have Clojure code that looks like this:
(if-let [source (get-stuff-from-database)]
(reduce +
(map somefn
(filter somepred (extract-data source))))
0) ; no data
Which is more functional in style. One thing you can do is to learn to
read these from right to left, which takes a bit of practice, but pays
off in the end, in my opinion. The ->> and -> macros are sometimes
useful for transforming the right-to-left -readable forms into forms
that look more like pipelines:
(->> (extract-data source)
(filter somepred)
(map somefn)
(reduce +))
There's no need for temporary names here. If a step needs explanation,
just add comments.
Hope this helps.
--
Jarkko
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