sg-calc.pl

#!/usr/bin/perl
use v5.14;

my $input_string;

say "Hello! Input string as \"x + y\" or \"sin x\" \n";
say 'You can use "+", "-", "*", "\", "**", "sin", "cos", "tan"';
$input_string = <STDIN>;
my ($first_arg, $second_arg, $third_arg) = split ' ', $input_string;

my %algebra = (
	'+'  => sub {$first_arg + $third_arg},
	'-'  => sub {$first_arg - $third_arg},
	'*'  => sub {$first_arg * $third_arg},
	'/'  => sub {$first_arg / $third_arg},
	'**' => sub {$first_arg**$third_arg},
);

my %trigonometry;
%trigonometry = (
	'sin' => sub {sin $second_arg},
	'cos' => sub {cos $second_arg},
	'tan' => sub {$trigonometry{sin}->() / $trigonometry{cos}->()},
);

sub algebra {$algebra{$second_arg}}

sub trigonometry {$trigonometry{$first_arg}}

sub wrong_op {
	sub {"The string entered in the incorrect form."}
}

my $op = ($input_string =~ m/^\d/ ? algebra() : trigonometry()) || wrong_op();

say $op->();