How can loop through perl constant

use constant NUCLEOTIDES => [ qw{ A C G T } ];

foreach (@{+NUCLEOTIDES}) {
    print;
}

Though beware: Although NUCLEOTIDES is a constant, the elements of the referenced array (e.g. NUCLEOTIDES->[0]) can still be modified.

Why not make your constant return a list?

sub NUCLEOTIDES () {qw(A C G T)}

print for NUCLEOTIDES;

or even a list in list context and an array ref in scalar context:

sub NUCLEOTIDES () {wantarray ? qw(A C G T) : [qw(A C G T)]}

print for NUCLEOTIDES;

print NUCLEOTIDES->[2];

if you also need to frequently access individual elements.

If you want to use the constant pragma, then you can just say

#!/usr/bin/perl

use strict;
use warnings;

use constant NUCLEOTIDES => qw/A C G T/;

for my $nucleotide (NUCLEOTIDES) {
   print "$nucleotide\n";
}

The item on the right of the fat comma (=>) does not have to be a scalar value.

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