challenge 027

4 files changed, 134 insertions, 0 deletions

diff --git a/challenge-027/markus-holzer/README b/challenge-027/markus-holzer/README
index 64aaa503e7..2000655be2 100644
--- a/challenge-027/markus-holzer/README
+++ b/challenge-027/markus-holzer/README
@@ -1 +1,6 @@
 Solutions by Markus Holzer.
+
+Solution #2 only works on the current developer branch and uses a module I wrote 
+Please see https://github.com/holli-holzer/perl6-Scalar-History
+To be on CPAN soon
+
diff --git a/challenge-027/markus-holzer/perl6/ch-1.pl6 b/challenge-027/markus-holzer/perl6/ch-1.pl6
new file mode 100644
index 0000000000..4c7e3b5448
--- /dev/null
+++ b/challenge-027/markus-holzer/perl6/ch-1.pl6
@@ -0,0 +1,27 @@
+multi sub MAIN( Int:D $x1, Int:D $y1, Int:D $x2, Int:D $y2, Int:D $x3, Int:D $y3, Int:D $x4, Int:D $y4 )
+{
+    with intersection( $x1, $y1, $x2, $y2, $x3, $y3, $x4, $y4 ) -> ($x, $y) 
+    { 
+        say "The intersection is at $x, $y.";
+    } 
+    else 
+    { 
+        say .exception.message;
+    }
+}
+
+
+sub intersection( Int \x1, Int \y1, Int \x2, Int \y2, Int \x3, Int \y3, Int \x4, Int \y4 )
+{
+    CATCH { default { fail "Lines are parallel or identical" } }
+    
+    return (
+        eager # potential for division by zero, 
+            ( (x1 * y2 - y1 * x2 ) * (x3 - x4) - (x1 - x2) * (x3 * y4 - y3*x4) ) div
+            ( (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4) ),
+
+        eager # without eager, laziness will bite us later
+            ( (x1 * y2 - y1 * x2) * (y3 - y4) - (y1 -y2) * (x3*y4 - y3 * x4) ) div
+            ( (x1 - x2) * (y3 - y4) - (y1 - y2) * (x2 - x4) )
+    );
+}
diff --git a/challenge-027/markus-holzer/perl6/ch-2.pl6 b/challenge-027/markus-holzer/perl6/ch-2.pl6
new file mode 100644
index 0000000000..d3bea23017
--- /dev/null
+++ b/challenge-027/markus-holzer/perl6/ch-2.pl6
@@ -0,0 +1,9 @@
+use Test;
+use Scalar::History; # See the README
+
+my Int $x := Scalar::History.create(10, Int);
+$x = 20;
+$x -= 5;
+
+ok( $x == 15 );
+is-deeply( $x.VAR.get-history, (10, 20) );
\ No newline at end of file
diff --git a/challenge-027/markus-holzer/perl6/lib/Scalar/History.pm6 b/challenge-027/markus-holzer/perl6/lib/Scalar/History.pm6
new file mode 100644
index 0000000000..13c8346424
--- /dev/null
+++ b/challenge-027/markus-holzer/perl6/lib/Scalar/History.pm6
@@ -0,0 +1,93 @@
+use Test;
+
+my $minumum-version = Version.new('2019.07.1.357.gd.00674.b.31');
+
+die "Scalar::History requires $minumum-version or later"
+    if ( $*PERL.compiler.version cmp $minumum-version ) == Less;
+
+class Scalar::History::Proxy is Proxy
+{
+    has @!history;
+    has $!position;
+
+    # This is needed for now since the standard ways
+    # like assigning in the `has` statement, TWEAK
+    # and BUILD don't work with `Proxy`
+
+    method new( :&FETCH!, :&STORE!, *%_ ) is raw
+    {
+        my $self := self.Proxy::new( :&FETCH, :&STORE );
+        $self.VAR.TWEAK( |%_ );
+        $self
+    }
+
+    method TWEAK( :$!position = 0 ) {
+        # yadayada
+    }
+
+    method current-value( \SELF: )
+    {
+        @!history[ $!position ]
+    }
+
+    method latest-value( \SELF: )
+    {
+        @!history[ *-1 ]
+    }
+
+    method get-history( \SELF: Bool :$all = False )
+    {
+        my $to-index = $all ?? @!history.elems - 1 !! $!position;
+        @!history[ ^$to-index ]
+    }
+
+    method reset-history( \SELF: )
+    {
+        @!history = ();
+        $!position = 0;
+    }
+
+    method forward-history( \SELF: $steps )
+    {
+        $!position = $!position + $steps;
+        $!position = @!history.elems - 1
+            if $!position >= @!history.elems;
+        $!position;
+    }
+
+    method rewind-history( \SELF: $steps )
+    {
+        $!position = $!position - $steps;
+        $!position = 0
+            if $!position < 0;
+        $!position;
+    }
+
+    method store-value( \SELF: $new-value, $register-duplicates )
+    {
+        # Forget stuff after rewind
+        if @!history.elems > $!position + 1
+        {
+            @!history.splice( $!position + 1 );
+        }
+
+        if !($new-value eqv SELF.current-value) || $register-duplicates
+        {
+            @!history.push( $new-value );
+            $!position = @!history.elems - 1;
+        }
+    }
+}
+
+class Scalar::History
+{
+    method create( $value, ::T $type = Any, Bool :$register-duplicates = False )
+    {
+        return-rw Scalar::History::Proxy.new(
+            FETCH => method ( \SELF: ) {
+                SELF.current-value() },
+            STORE => method ( \SELF: T $new-value ) {
+                SELF.store-value( $new-value, $register-duplicates ); }
+        ) = $value;
+    }
+}
\ No newline at end of file