add perl6 code for chapters 1-4 (#49)

04_quicksort/perl6/01_loop_sum.p6

@@ -0,0 +1,13 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+sub sum(@arr) {
+    my $total = 0;
+    for @arr {
+        $total += $_;
+    }
+    return $total;
+}
+
+my @arr = 1, 2, 3, 4;
+say sum(@arr);

04_quicksort/perl6/02_recursive_sum.p6

@@ -0,0 +1,8 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+multi sum([]) { 0 };
+multi sum(@arr) { @arr[0] + sum(@arr[1..*]) }
+
+my @arr = 1,2,3,4,5;
+say sum(@arr);

04_quicksort/perl6/03_recursive_count.p6

@@ -0,0 +1,8 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+multi count([]) { 0 }
+multi count(@arr) { 1 + count(@arr[1..*]) }
+
+my @arr = 1,2,3,4,5;
+say count(@arr);

04_quicksort/perl6/04_recursive_max.p6

@@ -0,0 +1,11 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+sub my-max(@arr) {
+    if @arr.elems == 2 { return (@arr[0] > @arr[1]) ?? @arr[0] !! @arr[1] }
+    my $sub-max = my-max(@arr[1..*]);
+    return (@arr[0] > $sub-max) ?? @arr[0] !! $sub-max;
+}
+
+my @arr = 1,2,3,4,5;
+say my-max(@arr);

04_quicksort/perl6/05_quicksort.p6

@@ -0,0 +1,21 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+sub quicksort(@arr) {
+    if @arr.elems < 2 {
+        # base case, arrays with 0 or 1 element are already "sorted"
+        return @arr;
+    }
+    else {
+        # recursive case
+        my $pivot = @arr[0];
+        # sub-array of all the elements less than the pivot
+        my @less = (gather for @arr[1..*] { take $_ if $_ <= $pivot });
+        # sub-array of all the elements greater than the pivot
+        my @greater = (gather for @arr[1..*] { take $_ if $_ > $pivot });
+        return (|quicksort(@less), $pivot, |quicksort(@greater));
+    }
+}
+
+my @arr = 10, 5, 2, 3;
+say quicksort(@arr);