Solution to task 2

1 files changed, 47 insertions, 0 deletions

diff --git a/challenge-108/jo-37/perl/ch-2.pl b/challenge-108/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use Math::Prime::Util qw(vecsum stirling);
+
+our $tests;
+
+run_tests() if $tests;	# does not return
+
+die <<EOS unless @ARGV == 1;
+usage: $0 [-tests] [num]
+
+-tests
+    run some tests
+
+num
+    print first <num> Bell numbers.
+
+EOS
+
+
+### Input and Output
+
+say "$_  ", B($_) for 0 .. $ARGV[0] - 1;
+
+
+### Implementation
+
+# Facing this task after having played with Math::Prime::Util for some
+# weeks, the module shouts: "Use me!"  And in fact: The Bell numbers
+# appear as an example.  This looks like a one week leave.
+# Taking a verbatim copy from the module's POD.
+
+sub B { my $n = shift; vecsum(map { stirling($n,$_,2) } 0..$n) }
+
+### Examples and tests
+
+sub run_tests {
+    my $i = 0;
+    for (1, 1, 2, 5, 15, 52, 203, 877, 4140, 21147) {
+        is B($i++), $_;
+    }
+
+    done_testing;
+    exit;
+}