use strict;
use warnings;

my $str = "a,b=c,e=#f";

my @result = map {
    /(\w+)(=(#?)(\w+))?/;
    defined $3 && $3 eq '#' ? "$1=>fn($4)" :
    defined $2 ? "$1=>$4"
               : "$1=>fn($1)"
    } split ',', $str;

print "@result";

##</code><code>##

a=>fn(a) b=>c e=>fn(f)