Solution to task 1

1 files changed, 113 insertions, 0 deletions

diff --git a/challenge-095/jo-37/perl/ch-1.pl b/challenge-095/jo-37/perl/ch-1.pl
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+++ b/challenge-095/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use warnings FATAL => 'all';
+use Scalar::Util 'looks_like_number';
+use experimental 'signatures';
+
+our ($tests, $examples, $verbose);
+
+run_tests() if $tests || $examples;    # does not return
+
+say(<<EOS), exit unless @ARGV;
+usage: $0 [-examples] [-tests] [--] [string]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+-verbose
+    print diagnostic information
+
+string
+    string to test if it represents a palindrome number
+
+EOS
+
+### Input and Output
+
+my $ret = palindrome_number($ARGV[0]);
+
+if ($verbose) {
+    say "got $ARGV[0]" if $verbose;
+    if (!defined $ret) {
+        say 'is not a number';
+    } else {
+        say "has value ", 0 + $ARGV[0];
+        if ($ret eq '') {
+            say 'reverse value is not a number';
+        } elsif ($ret) {
+            say "is palindrome";
+        } else {
+            say "is not palindrome";
+        }
+    }
+}
+
+say 0 + !!$ret;
+
+### Implementation
+
+# The concept of "number palindromes" needs further specifications to be
+# well defined because "palindromic" is a string property and there is no
+# unique string representation of a number.  Following the examples I'll
+# take the decimal representation of a number that has to form a palindrome.
+# Though there seems to be some consensus on considering integer numbers
+# only, *any* numeric value is allowed here.
+#
+# A string shall be considered as palindromic number, iff the
+# transformation chain
+#   numify->stringify->reverse->numify->stringify 
+# resembles the input string. (All transformations from a Perl view.)
+#
+# This sub uses different false return values to signal the failed test:
+# - undef for a non-numeric input string
+# - the empty string for a non-numeric reversed numified input string
+# - zero for a numeric forward and backward value that is not a palindrome
+#   number
+sub palindrome_number ($str) {
+    return unless looks_like_number $str;
+    my $reverse = reverse $str + 0;
+    return '' unless looks_like_number $reverse;
+
+    0 + ($str eq $reverse + 0);
+}
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+        ok palindrome_number(1221), 'example 1: 1221 is palindrome';
+        ok !palindrome_number(-101), 'example 2: -101 is not palindrome';
+        ok !palindrome_number(90), 'example 3: 90 is not palindrome';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+        for my $str (qw(21e12 1.221e3 0012100 00121 0012.2100)) {
+            ok !palindrome_number($str), "$str is not palindrome";
+        }
+        for my $str (qw(12.21 1221)) {
+            ok palindrome_number($str), "$str is palindrome";
+        }
+
+        # specific return codes
+        is palindrome_number('1O2O1'), U(), 'not a number';
+        is palindrome_number('-101'), '', 'reverse not a number';
+        is palindrome_number('1e-21'), '', 'reverse not a number';
+        is palindrome_number('12327'), 0, 'not palindrome';
+        is palindrome_number('+121.0'), 0, 'not palindrome';
+        is palindrome_number('121'), 1, 'palindrome';
+
+        # exotic cases: NaN vs. nan
+        is palindrome_number('NaN'), 0, 'NaN is numeric';
+        is palindrome_number('nan'), 1, 'possibly the strangest case';
+    }
+
+    done_testing;
+    exit;
+}