Re^3: howto map/grep a complex structure

[AnomalousMonk]

I can't say I agree with the overall approach of trippledubs here, but I think the use of prototypes therein can be said to have a constructive and well understood purpose.

As written,  collectLeaves() is recursive, and within the function the calls such as
    &collectLeaves( $_, $leaves ) for ( @{$ds} );
serve the purpose of suppressing prototype checking so the  $leaves reference can be passed in recursive calls.

Outside the function, prototyping allows calls like
    my @wanted = grep { $_ == 7 } collectLeaves $hashref1, collectLeaves $hashref2;
to be made, while
    ... collectLeaves($hashref1, $hashref2) ...
will fail to compile.

c:\@Work\Perl\monks>perl -wMstrict -le
"sub S ($) { return $_[0] + print 0+@{$_[0]}, ' elements in ', 0+$_[0]
+; }
 ;;
 print S [], S [42], 33;
"
0 elements in 7450732
1 elements in 30219348
74507333021934933

(But  S([],[42]) will not compile.)

Again, I don't say I necessarily agree with the approach, but I cannot agree that prototyping has been sprinkled thoughtlessly onto the code as a kind of magical correctness dust, as we have often seen. OTOH, I agree with you that the response of future maintainers to this code (or recursive functions in general) is a valid concern.

[trippledubs]

Hi Anomalous! Thank you for discerning that it is not on accident! Why do you not necessarily agree with this approach? The nihilist in me says I shouldn't care yet the objectivist wants to improve..

[AnomalousMonk]

Anonymonk originally posted a for-loop approach to processing a data structure, then asked for ways to make it more "elegant" with map and grep. Several Monks opined that, for several reasons, the for-loop code was perfectly good as it was and needed no ornamentation. I strongly agree.

Anon then replied "Ok, point taken, but I'd still appreciate some map/grep examples." The implication I took was that approaches other than map/grep would also be of interest. Several Monks responded with examples, including your recursive approach. I strongly approve these efforts; this is a teaching/learning site, after all.

So we come down to two questions that are somewhat at cross-purposes: "What's the best code for this specific application?" and "What other sorts of algorithmic approaches might be used in similar situations?" The answer to the first question is "The code we started with." The answer to the second is "There are lots of approaches that might be used with profit, including the one posted by trippledubs here!" I hope the divergence of the two questions helps explain the half-hearted nature of my approval.