1 files changed, 69 insertions, 0 deletions
diff --git a/challenge-153/jo-37/perl/ch-1.pl b/challenge-153/jo-37/perl/ch-1.pl
new file mode 100755
index 0000000000..861e8d0a13
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+++ b/challenge-153/jo-37/perl/ch-1.pl
@@ -0,0 +1,69 @@
+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use bigint;
+use Coro::Generator;
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [N]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+N
+    Print the first N left factorials.
+
+EOS
+
+
+### Input and Output
+
+main: {
+    my $left_factorial = gen_left_factorial();
+    say $left_factorial->() for 1 .. $ARGV[0];
+}
+
+
+### Implementation
+
+# Build a generator for left factorials
+sub gen_left_factorial {
+    my ($index, $factorial, $left_factorial) = (0, 1, 1);
+
+    generator {
+        yield $left_factorial;
+        yield $left_factorial += ($factorial *= ++$index) while 1;
+    }
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        my $left_factorial = gen_left_factorial();
+        is [map $left_factorial->(), 1 .. 10],
+            [1, 2, 4, 10, 34, 154, 874, 5914, 46234, 409114], 'task 1';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        my $left_factorial = gen_left_factorial();
+        $left_factorial->() for 1 .. 21;
+        is $left_factorial->(), 53652269665821260314, 'from OEIS';
+	}
+
+    done_testing;
+    exit;
+}