Challenge 143 task 1

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diff --git a/challenge-143/jo-37/perl/ch-1.pl b/challenge-143/jo-37/perl/ch-1.pl
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+++ b/challenge-143/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -Ts
+
+use v5.24;
+use Test2::V0;
+use experimental 'signatures';
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [--] [EXPR]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+EXPR
+    arithmetic expression made of digits, whitespace, '+', '-', '*' and
+    parentheses
+
+EOS
+
+
+### Input and Output
+
+say calculator(shift);
+
+
+### Implementation
+
+sub calculator ($s) {
+    # Laundering the input string:
+	$s =~ /^([-+*\d\s()]*)$/ or return "expression invalid: $s";
+    my $result = eval $1;
+    $@ ? $@ : $result;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+        is calculator('10 + 20 - 5'), 25, 'example 1';
+        is calculator('(10 + 20 - 5) * 2'), 50, 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+	}
+
+    done_testing;
+    exit;
+}