Implement squish() and .squish(), as per S32/Containers

src/core/Any.pm

@@ -17,6 +17,7 @@ my class Any {
     method classify($test)   { {}.classify(   $test, self.list ) }
     method categorize($test) { {}.categorize( $test, self.list ) }
     method uniq() { self.list.uniq }
+    method squish() { self.list.squish }
     method infinite() { Mu }
     method flat() { nqp::p6list(nqp::list(self), List, Bool::True) }
     method hash() { my % = self }
@@ -786,6 +787,9 @@ multi categorize( $test, *@items ) { {}.categorize( $test, @items ) }
 proto uniq(|) { * }
 multi uniq(*@values) { @values.uniq }
 
+proto squish(|) { * }
+multi squish(*@values) { @values.squish }
+
 proto sub sort(|) {*}
 multi sub sort(*@values)      {
     @values.at_pos(0).^does(Callable)

src/core/List.pm

@@ -335,6 +335,15 @@ my class List does Positional {
         }
     }
 
+    my @secret;
+    method squish() {
+        my $last = @secret;
+        gather sink for @.list {
+            take $_ if $_ !=== $last;
+            $last = $_;
+        }
+    }
+
     multi method gist(List:D:) { join ' ', map { $_.gist }, @(self) }
     multi method perl(List:D \SELF:) {
         self.gimme(*);

t/spectest.data

@@ -637,6 +637,7 @@ S32-list/reverse.t
 S32-list/roll.t
 S32-list/sort.t
 S32-list/uniq.t
+S32-list/squish.t
 S32-num/abs.t
 S32-num/base.t
 S32-num/complex.t