> (a) Avoid recursion, unless you are memoizing the results.
I wonder about this one. A recursion whose results
are atoms (or involve small amounts of data) could
be inefficient without memoization. Otherwise there
is nothing much wrong with recursion in J. e.g.
perm=: 3 : 0
if. y do. ,/ (0,.perm&.<: y) {"2 1 \:"1 =i.y else. i.1 0 end.
)
perm 3
0 1 2
0 2 1
1 0 2
1 2 0
2 0 1
2 1 0
----- Original Message -----
From: John Randall <[EMAIL PROTECTED]>
Date: Tuesday, May 1, 2007 10:52 am
Subject: Re: [Jprogramming] Moving past the alchemist stage
> Geoff:
>
> I think sticking to completely tacit is a hard row to hoe: it
> makes a
> steep learning curve even steeper. I would begin with explicit and
> gradually mix in more tacit.
>
> There are a lot of things in J that are completely non-obvious if you
> are coming from another language. Here are a few that have helped me.
>
> (a) Avoid recursion, unless you are memoizing the results.
>
> (b) Learn to use the power conjunction, especially in the form
> f^:g^:_ .
>
> (c) Avoid small selections: use #~f whenever possible. I almost never
> use @. .
>
> I have benefited greatly from the J Phrases: they are both useful and
> instructive.
>
> When it comes to projecteuler.net, don't be put off by the J
> solutions. I had exactly the same experience as you: my J code was
> about 50 times longer and looked nothing like the experts'. I felt
> stupid. I have learned a lot more since, but I also know that
> many of
> the posted solutions are highly polished for brevity or efficiency but
> not transparency.
>
> Most of the more difficult problems are set up so that the warmup
> example can be done naively, but the actual problem requires something
> better, either mathematically or computationally. For example, #146
> is mathematically easy, but computationally difficult. It took me a
> long time to get a solution that came in under a minute. On the other
> hand, the most recent problem (#152) is computationally easy once you
> have done the math, which is highly nontrivial. You can tell this
> from the small number of solutions 4 days after the problem came out.
> If it were amenable to brute force, there would be more.
>
> Best wishes,
>
> John
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