--- /dev/null
+#!perl
+
+use Test::More tests => 13;
+
+use warnings FATAL => 'all';
+use strict;
+
+use Function::Parameters {
+ fun => {
+ check_argument_count => 1,
+ },
+};
+
+fun filter($f = fun ($x) { 1 }, @xs) {
+ !@xs
+ ? ()
+ : (($f->($xs[0]) ? $xs[0] : ()), filter $f, @xs[1 .. $#xs])
+}
+
+is_deeply [filter], [];
+is_deeply [filter fun { 1 }, 2 .. 3], [2 .. 3];
+is_deeply [filter fun ($x) { $x % 2 }, 1 .. 10], [1, 3, 5, 7, 9];
+
+fun fact($k, $n) :(&$) {
+ $n < 2
+ ? $k->(1)
+ : fact { $k->($n * $_[0]) } $n - 1
+}
+
+is +(fact { "~@_~" } 5), "~120~";
+is +(fact { $_[0] / 2 } 6), 360;
+
+fun write_to($ref) :(\$) :lvalue { $$ref }
+
+{
+ my $x = 2;
+ is $x, 2;
+ write_to($x) = "hi";
+ is $x, "hi";
+ write_to($x)++;
+ is $x, "hj";
+}
+
+{
+ my $c = 0;
+ fun horf_dorf($ref, $val = $c++) :(\@;$) :lvalue {
+ push @$ref, $val;
+ $ref->[-1]
+ }
+}
+
+{
+ my @asdf = "A";
+ is_deeply \@asdf, ["A"];
+ horf_dorf(@asdf) = "b";
+ is_deeply \@asdf, ["A", "b"];
+ ++horf_dorf @asdf;
+ is_deeply \@asdf, ["A", "b", 2];
+ horf_dorf @asdf, 100;
+ is_deeply \@asdf, ["A", "b", 2, 100];
+ splice @asdf, 1, 1;
+ horf_dorf(@asdf) *= 3;
+ is_deeply \@asdf, ["A", 2, 100, 6];
+}