Re^2: Concise foreach expression

which means you won't have much use of nested loops with map

Could you explain what you mean there? map localizes $_, so nested maps are not a problem. Code like the following (admittedly contrived) snippet works as expected ($_ is not clobbered by the inner map):

my @list = (
    ["Barney", "Rubble"],
    ["Fred", "Flintstone"],
    ["Betty", "Rubble"],
    ["Wilma", "Flintstone"]
);

map {
    say "Outer map before: @$_";
    map { 1 } @$_;
    say "Outer map after : @$_";
} @list;
[download]

But perhaps there's other pitfalls, so I'd be grateful for any enlightenment.

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Re^3: Concise foreach expression by choroba (Cardinal) on Aug 29, 2014 at 17:14 UTC
The problem happens when you need to use the $_ from the outer map in the inner map, as in the following contrived example: `my %tree = ( child1 => {}, child2 => { grandchild1 => { brood3 => {} }, grandchild2 => { brood1 => {}, brood2 => {} }, }, ); say for 'Grandchildren:', map { my $x = $_; # <--- remove me! "$_: " . (ref $tree{$_} ? join ', ' => map keys %{ $tree{$x}{$_} }, keys %{ $tree{$_} } : q()) } keys %tree;` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l]
Re^3: Concise foreach expression by LanX (Saint) on Aug 29, 2014 at 17:00 UTC
> Could you explain what you mean there? I was talking about chaining `map`s or `for`s to simulate nested foreach loops. I.o.w. list comprehensions are very hard to implement in Perl without nested blocks. e.g. try to implement this Python example for "Pythagorean triples" w/o nesting `>>> [(x,y,z) for x in range(1,30) for y in range(x,30) for z in range( +y,30) if x2 + y2 == z**2] [(3, 4, 5), (5, 12, 13), (6, 8, 10), (7, 24, 25), (8, 15, 17), (9, 12, + 15), (10, 24, 26), (12, 16, 20), (15, 20, 25), (20, 21, 29)]` [download] Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)}	[reply] [d/l]
Re^4: Concise foreach expression by AppleFritter (Vicar) on Aug 29, 2014 at 17:21 UTC
Ah, yes, I see what you mean.	[reply]
Re^5: Concise foreach expression by LanX (Saint) on Aug 29, 2014 at 17:42 UTC
FWIW I once implemented a ( Monad style ;-) approach to emulate this `@results = take { [$a,$b,$c] if $a2 +$b2 ==$c2 } from {1..30} $a from {1..$a} $b from {1...$b} $c` `take(&$)` and `from(&$$)` where just ordinary functions passing iterators around. The problem I couldn't solve was a DRY scoping of the variables, to be strict I needed to surround the whole expression with `{ my($a,$b,$c); ... }` [download] `my` declarations don't effect the scope of the same line. :( Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)} update hmm maybe this syntax is acceptable? ~~`from { 1..30} my $a from {1..$a} my $b from { 1...$b} my $c; @results = take { [$a,$b,$c] if $a2 +$b2 ==$c2 }`~~ ~~[download]~~ ~~when called from void context `from()` could put the iterator into `$_` , and `take()` could read it again from `$_` if called with just one block arg...~~ never mind doesn't work.	[reply] [d/l] [select]

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