Morse Code Decoder in Perl - arrays

Question

I am trying to teach myself Perl and I have been struggling... Last night I did a program to calculate the average of a set of numbers that the user provided in order to learn about lists and user input so today I thought I would do a Morse Code decoder to learn about Hashes. I have looked through the book that I bought and it doesn't really explain hashes very well... it actually doesn't explain a lot of things very well. Any help would be appreciated!
Anyways, I am wanting to write a program that decodes the morse code that the user inputs. So the user would enter:
-.-.
.-
-
...
!
.-.
..-
.-..
.
The exclamation point would signify a separate word. This message would return "Cats Rule" to the user. Below is the code I have so far... Remember.. I have been programming in perl for under 24 hours haha.
Code:
use 5.010;
my %morsecode=(
'.-' =>'A', '-...' =>'B', '-.-.' =>'C', '-..' =>'D',
'.' =>'E', '..-.' =>'F', '--.' =>'G', '....' =>'H',
'..' =>'I', '.---' =>'J', '-.-' =>'K', '.-..' =>'L',
'--' =>'M', '-.' =>'N', '---' =>'O', '.--.' =>'P',
'--.-' =>'Q', '.-.' =>'R', '...' =>'S', '-' =>'T',
'..-' =>'U', '...-' =>'V', '.--' =>'W', '-..-' =>'X',
'-.--' =>'Y', '--..' =>'Z', '.----' =>'1', '..---' =>'2',
'...--' =>'3', '....-' =>'4', '.....' =>'5', '-....' =>'6',
'--...' =>'7', '---..' =>'8', '----.' =>'9', '-----' =>'0',
'.-.-.-'=>'.', '--..--'=>',', '---...'=>':', '..--..'=>'?',
'.----.'=>'\'', '-...-' =>'-', '-..-.' =>'/', '.-..-.'=>'\"'
);
my #k = keys %morsecode;
my #v = values %morsecode;
say "Enter a message in morse code separated by a line. Use the exclamation point (!) to separate words. Hit Control+D to signal the end of input.";
my #message = <STDIN>;
chomp #message;
my $decodedMessage = encode(#message);
sub encode {
foreach #_ {
if (#_ == #k) {
return #k;
#This is where I am confused... I am going to have to add the values to an array, but I don't really know how to go about it.
}
else if(#_ == '!') {return ' '}
else
{
return 'Input is not valid';
}
}
}

Answer 1

Your code contains two syntactic errors: foreach requires a list to iterate over; this means parens. Unlike C and other languages, Perl doesn't support else if (...). Instead, use elsif (...).
Then there are a few semantic mistakes: The current value of an iteration is stored in $_. The array #_ contains the arguments of the call to your function.
Perl comparse strings and numbers differently:
Strings Numbers
eq ==
lt <
gt >
le <=
ge >=
ne !=
cmp <=>
Use the correct operators for the task at hand, in this case, the stringy ones.
(Your code #_ == #k does something, namely using arrays in numeric context. This produces the number of elements, which is subsequenty compared. #_ == '!' is just weird.)
What you really want to do is to map the inputted values to a list of characters. Your hash defines this mapping, but we want to apply it. Perl has a map function, it works like
#out_list = map { ACTION } #in_list;
Inside the action block, the current value is available as $_.
We want our action to look up the appropriate value in the hash, or include an error message if there is no mapping for the input string:
my #letters = map { $morsecode{$_} // "<unknown code $_>" } #message;
This assumes ! is registered as a space in the morsecode hash.
We then make a single string of these letters by joining them with the empty string:
my $translated_message = join "", #letters;
And don't forget to print out the result!
The complete code:
#!/usr/bin/perl
use strict; use warnings; use 5.012;
my %morsecode=(
'.-' =>'A', '-...' =>'B', '-.-.' =>'C', '-..' =>'D',
'.' =>'E', '..-.' =>'F', '--.' =>'G', '....' =>'H',
'..' =>'I', '.---' =>'J', '-.-' =>'K', '.-..' =>'L',
'--' =>'M', '-.' =>'N', '---' =>'O', '.--.' =>'P',
'--.-' =>'Q', '.-.' =>'R', '...' =>'S', '-' =>'T',
'..-' =>'U', '...-' =>'V', '.--' =>'W', '-..-' =>'X',
'-.--' =>'Y', '--..' =>'Z', '.----' =>'1', '..---' =>'2',
'...--' =>'3', '....-' =>'4', '.....' =>'5', '-....' =>'6',
'--...' =>'7', '---..' =>'8', '----.' =>'9', '-----' =>'0',
'.-.-.-'=>'.', '--..--'=>',', '---...'=>':', '..--..'=>'?',
'.----.'=>'\'', '-...-' =>'-', '-..-.' =>'/', '.-..-.'=>'"',
'!' =>' ',
);
say "Please type in your morse message:";
my #codes = <>;
chomp #codes;
my $message = join "", map { $morsecode{$_} // "<unknown code $_>" } #codes;
say "You said:";
say $message;
This produces the desired output.

Answer 2

There's a lot of value in learning the how and why, but here's the what:
sub encode {
my $output;
foreach my $symbol (#_) {
my $letter = $morsecode{$symbol};
die "Don't know how to decode $symbol" unless defined $letter;
$output .= $letter
}
return $output;
}
or even as little as sub encode { join '', map $morsecode{$_}, #_ } if you're not too worried about error-checking. #k and #v aren't needed for anything.

Answer 3

Searching for values in hashes is a very intense job, you are better of by just using a reverse hash. You can easily reverse a hash with the reverse function in Perl. Also, while watching your code I have seen that you will be able to enter lower-case input. But while searching in hashes on keys, this is case-sensitive. So you will need to uppercase your input. Also, I do not really like the way to "end" an STDIN. An exit word/sign would be better and cleaner.
My take on your code
my %morsecode=(
'.-' =>'A', '-...' =>'B', '-.-.' =>'C', '-..' =>'D',
'.' =>'E', '..-.' =>'F', '--.' =>'G', '....' =>'H',
'..' =>'I', '.---' =>'J', '-.-' =>'K', '.-..' =>'L',
'--' =>'M', '-.' =>'N', '---' =>'O', '.--.' =>'P',
'--.-' =>'Q', '.-.' =>'R', '...' =>'S', '-' =>'T',
'..-' =>'U', '...-' =>'V', '.--' =>'W', '-..-' =>'X',
'-.--' =>'Y', '--..' =>'Z', '.----' =>'1', '..---' =>'2',
'...--' =>'3', '....-' =>'4', '.....' =>'5', '-....' =>'6',
'--...' =>'7', '---..' =>'8', '----.' =>'9', '-----' =>'0',
'.-.-.-'=>'.', '--..--'=>',', '---...'=>':', '..--..'=>'?',
'.----.'=>'\'', '-...-' =>'-', '-..-.' =>'/', '.-..-.'=>'\"'
);
my %reversemorse = reverse %morsecode;
print "Enter a message\n";
chomp (my $message = <STDIN>);
print &encode($message);
sub encode{
my $origmsg = shift(#_);
my #letters = split('',$origmsg);
my $morse = '';
foreach $l(#letters)
{
$morse .= $reversemorse{uc($l)}." ";
}
return $morse;
}