Making 2nd Degree Polys Given a Triplet - perl

Question

The purpose of this code is to make a subroutine that takes three coefficients k2, k1 , and k0 and returns an anonymous function/subroutine that takes one argument x and returns a string representation of the second degree polynomial with the given coefficients and its value at x, i.e., k2*x^2 + k1*x + k0.
As of right now, it returns the message "Can't use string ("6") as an ARRAY ref while "strict refs" is in use"
Does anyone see what I'm messing up?
use strict;
use warnings;
use 5.10.0;
sub make_2nd_degree_poly {
my($k2, $k1, $k0) = #_;
my $n = $_[0];
return sub {
return ($k2 . 'x^2 . ' . $k1 . 'x + ' . $k0 . ' at x = ' . $n,
$k2 * $n ** 2 + $k1 *$n + $k0
);
}
}
my #triplet0 = (1, 2, 3);
my #triplet1 = (4, 5, 6);
my $p1 = make_2nd_degree_poly(#triplet0);
my $p2 = make_2nd_degree_poly(#triplet1);
print "#{$p1->(1)}\n";
print "#{$p2->(2)}\n";
Next part of the issue: I need to write a function/sub gen_2nd_deg_polys that takes a list of 3-tuples and returns a list of anonymous 2nd
degree polynomials.
polys = gen_2nd_deg_polys([(1, 2, 3), (4, 5, 6)])
THIS SHOULD BE MY OUTPUT:
('1x^2 + 2x + 3 at x = 1 is ', 6)
('4x^2 + 5x + 6 at x = 2 is ', 32)
How can I extend this program to accomplish this task?
sub gen_2nd_deg_polys {
return map(make_2nd_degree_poly(#{$_}), #_);
}
my (#a) = #_;
#a = ([1..3],[4..6]);
my #p3 = gen_2nd_deg_polys(#a);
print #p3->(1);

Answer 1

You can't dereference something that's not a reference. Your created sub returns a list, make it return an anonymous array instead:
return sub {
[ "${k2}x^2 . $k1 x + $k0 at x = $n",
$k2 * $n ** 2 + $k1 *$n + $k0 ]
}
Or, return just one string:
return sub {
"${k2}x^2 . $k1 x + $k0 at x = $n "
. ($k2 * $n ** 2 + $k1 *$n + $k0)
}
Then, you need no dereference:
print $p1->(1), "\n";
print $p2->(2), "\n";
Update
Or, return a list, no dereference needed in such a case, but you might like to add a space in between the formula and the result:
return sub {
my $n = $_[0];
return "${k2}x^2 . $k1 x + $k0 at x = $n",
($k2 * $n ** 2 + $k1 *$n + $k0)
}
# ...
print join ' ', $p1->(1), "\n";
print join ' ', $p2->(2), "\n";
sub gen_2nd_deg_polys {
return map make_2nd_degree_poly(#$_), #_;
}
my #arr = ([1, 2, 3], [4, 5, 6]);
my #p3 = gen_2nd_deg_polys(#arr);
print join ' ', $_->(1), "\n" for #p3;

Answer 2

You can use references to force Perl to interpolate the return value of a function call inside double-quoted strings.So, here your #{} should contain [] to perl interpolate that you are returning an array reference.
You should do #{[]} in print to tell it you are returning an array reference which you are dreferencing using #{}.
Change your print statements to this. And then it should work:
print "#{[$p1->(1)]}\n";
print "#{[$p2->(2)]}\n";