Is it a palindrome?

Six words, read forwards and backwards. Guess which of them are palindromes before you run the program.

A palindrome is a word that reads the same from both ends, like level. This program takes six words and checks each of them.

Before you run it

Which of the six words are palindromes? Be careful with the first one: it starts with a capital letter.

The text

# Some words read the same from both ends.
my $count = 0;

for <Anna Level Riga Kayak Tallinn Rotor> {
    my $word = $_.lc;
    if $word eq $word.flip {
        say "$_ is a palindrome.";
        $count = $count + 1;
    }
    else {
        say "$_ is not. Backwards, it is " ~ $word.flip ~ '.';
    }
}

say "Palindromes found: $count";

Anna is a palindrome.
Level is a palindrome.
Riga is not. Backwards, it is agir.
Kayak is a palindrome.
Tallinn is not. Backwards, it is nnillat.
Rotor is a palindrome.
Palindromes found: 4

Words

• # — starts a comment. Raku ignores everything from # to the end of the line. Comments are for people.
• <Anna Level Riga Kayak Tallinn Rotor> — a list of words. Inside < >, every word separated by spaces becomes a string, so you don’t need quotes and commas.
• .lc — gives the string in lower case. It is the opposite of .uc.
• eq — compares two strings. It is true when they are exactly the same.
• .flip — gives the string backwards.
• ~ — joins two strings into one.

Reading notes

# Some words read the same from both ends.
my $count = 0;

The first line is a comment: it tells you what the program is about, and Raku skips it. The second line creates a counter that starts at zero.

for <Anna Level Riga Kayak Tallinn Rotor> {
    my $word = $_.lc;

The loop runs six times, once for each word in the list, and $_ holds the current word. The program makes a lower-case copy of it in $word. The word in $_ itself does not change.

Why lower case? Because 'Anna'.flip is annA, and Anna and annA are not the same string. After .lc, the program compares anna with anna.

    if $word eq $word.flip {
        say "$_ is a palindrome.";
        $count = $count + 1;
    }

If the word is the same forwards and backwards, the program says so and adds one to the counter. It prints $_, not $word, so you see the word with its capital letter.

    else {
        say "$_ is not. Backwards, it is " ~ $word.flip ~ '.';
    }

Otherwise, it prints the word backwards. Three strings are joined with ~: the text in double quotes, the flipped word, and a full stop.

Why not put $word.flip inside the double quotes? In a string, Raku replaces $word with its value, but it does not call .flip. You would see riga.flip instead of agir.

say "Palindromes found: $count";

After the loop, the program prints the counter.

Questions

1. How many lines does the program print?
2. What would the program say about Anna if the line were my $word = $_; without .lc?
3. What does say 'Riga'.flip; print?

Try this

Add the words Madam and Mississippi to the list. Before you run the program, decide what the last line will say.