solutions to exercise 1

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+#!/usr/bin/env perl6
+
+=begin SYNOPSIS
+
+Write a script to display months from the year 1900 to 2019 where you find 5 weekends
+i.e. 5 Friday, 5 Saturday and 5 Sunday.
+
+Usage:
+    $ perl6 ch-1.p6 --from=YYYY --to=YYYY
+
+Example output:
+    $ perl6 ch-1.p6 --from=1900 --to=2019
+    Found 119 months with 5 full weekends
+    1901: Mar
+    1902: Aug
+    1903: May
+    1904: Jan, Jul
+    ...
+    2017: Dec
+    2019: Mar
+    
+=end SYNOPSIS
+
+role MonthRole {
+    method has-five-full-weekends {
+        # The month must have 31 days.
+        return False unless self.days-in-month == 31;
+        # The month must begin on a Friday.
+        my $date = self.day == 1 ?? self !! Date.new( self.year, self.month, 1 );
+        return $date.day-of-week == 5;
+    }
+
+    method month-name-short {
+        given self.month {
+            when  1 { 'Jan' }
+            when  2 { 'Feb' }
+            when  3 { 'Mar' }
+            when  4 { 'Apr' }
+            when  5 { 'May' }
+            when  6 { 'Jun' }
+            when  7 { 'Jul' }
+            when  8 { 'Aug' }
+            when  9 { 'Sep' }
+            when 10 { 'Oct' }
+            when 11 { 'Nov' }
+            when 12 { 'Dec' }
+        }
+    }
+}
+
+sub find-months( $from, $to ) {
+    my @matches;
+    for $from .. $to -> $year {
+        for 1 .. 12 -> $month {
+            my $date = Date.new($year,$month,1) but MonthRole;
+            push @matches, $date if $date.has-five-full-weekends;
+        }
+    }
+    return @matches;
+}
+
+sub MAIN( :$from!, :$to! ) {
+    my @matches = find-months( $from, $to );
+    say "Found @matches.elems() months with 5 full weekends";
+    for @matches.classify( { .year } ).pairs.sort({ .key }) -> $pair {
+        say "{$pair.key}: { $pair.value>>.month-name-short.join(', ') }";
+    }
+}
+
+