Re: Concise foreach expression

[LanX]

You are trying to combine postfix foreach and postfix if and running into two problems:

1. they can't be chained
2. they can't use loop-vars other than $_

Your best bet for a concise expressions to be chained are map and grep

print grep { /test/ } @names

update

N.B.: you are still limited to $_

update

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

[AppleFritter]

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;

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

[choroba]

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;

[LanX]

> Could you explain what you mean there?

I was talking about chaining maps or fors 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 x**2 + y**2 == 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)]

[AppleFritter]

Ah, yes, I see what you mean.