# 4d47's solution

## to Roman Numerals in the Perl 6 Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Write a function to convert from normal numbers to Roman Numerals.

The Romans were a clever bunch. They conquered most of Europe and ruled it for hundreds of years. They invented concrete and straight roads and even bikinis. One thing they never discovered though was the number zero. This made writing and dating extensive histories of their exploits slightly more challenging, but the system of numbers they came up with is still in use today. For example the BBC uses Roman numerals to date their programmes.

The Romans wrote numbers using letters - I, V, X, L, C, D, M. (notice these letters have lots of straight lines and are hence easy to hack into stone tablets).

`````` 1  => I
10  => X
7  => VII
``````

There is no need to be able to convert numbers larger than about 3000. (The Romans themselves didn't tend to go any higher)

Wikipedia says: Modern Roman numerals ... are written by expressing each digit separately starting with the left most digit and skipping any digit with a value of zero.

To see this in practice, consider the example of 1990.

In Roman numerals 1990 is MCMXC:

1000=M 900=CM 90=XC

2008 is written as MMVIII:

2000=MM 8=VIII

## Resources

Remember to check out the Perl 6 documentation and resources pages for information, tips, and examples if you get stuck.

## Running the tests

There is a test suite and module included with the exercise. The test suite (a file with the extension `.t`) will attempt to run routines from the module (a file with the extension `.pm6`). Add/modify routines in the module so that the tests will pass! You can view the test data by executing the command `perl6 --doc *.t` (* being the name of the test suite), and run the test suite for the exercise by executing the command `prove6 .` in the exercise directory.

## Source

The Roman Numeral Kata http://codingdojo.org/cgi-bin/index.pl?KataRomanNumerals

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### roman-numerals.t

``````#!/usr/bin/env perl6
use v6;
use Test;
use JSON::Fast;
use lib \$?FILE.IO.dirname;
use RomanNumerals;
plan 19;

my \$c-data = from-json \$=pod.pop.contents;
for \$c-data<cases>.values {
is to-roman(.<input><number>), |.<expected description>;
}

=begin code
{
"exercise": "roman-numerals",
"version": "1.2.0",
"cases": [
{
"description": "1 is a single I",
"property": "roman",
"input": {
"number": 1
},
"expected": "I"
},
{
"description": "2 is two I's",
"property": "roman",
"input": {
"number": 2
},
"expected": "II"
},
{
"description": "3 is three I's",
"property": "roman",
"input": {
"number": 3
},
"expected": "III"
},
{
"description": "4, being 5 - 1, is IV",
"property": "roman",
"input": {
"number": 4
},
"expected": "IV"
},
{
"description": "5 is a single V",
"property": "roman",
"input": {
"number": 5
},
"expected": "V"
},
{
"description": "6, being 5 + 1, is VI",
"property": "roman",
"input": {
"number": 6
},
"expected": "VI"
},
{
"description": "9, being 10 - 1, is IX",
"property": "roman",
"input": {
"number": 9
},
"expected": "IX"
},
{
"description": "20 is two X's",
"property": "roman",
"input": {
"number": 27
},
"expected": "XXVII"
},
{
"description": "48 is not 50 - 2 but rather 40 + 8",
"property": "roman",
"input": {
"number": 48
},
"expected": "XLVIII"
},
{
"description": "49 is not 40 + 5 + 4 but rather 50 - 10 + 10 - 1",
"property": "roman",
"input": {
"number": 49
},
"expected": "XLIX"
},
{
"description": "50 is a single L",
"property": "roman",
"input": {
"number": 59
},
"expected": "LIX"
},
{
"description": "90, being 100 - 10, is XC",
"property": "roman",
"input": {
"number": 93
},
"expected": "XCIII"
},
{
"description": "100 is a single C",
"property": "roman",
"input": {
"number": 141
},
"expected": "CXLI"
},
{
"description": "60, being 50 + 10, is LX",
"property": "roman",
"input": {
"number": 163
},
"expected": "CLXIII"
},
{
"description": "400, being 500 - 100, is CD",
"property": "roman",
"input": {
"number": 402
},
"expected": "CDII"
},
{
"description": "500 is a single D",
"property": "roman",
"input": {
"number": 575
},
"expected": "DLXXV"
},
{
"description": "900, being 1000 - 100, is CM",
"property": "roman",
"input": {
"number": 911
},
"expected": "CMXI"
},
{
"description": "1000 is a single M",
"property": "roman",
"input": {
"number": 1024
},
"expected": "MXXIV"
},
{
"description": "3000 is three M's",
"property": "roman",
"input": {
"number": 3000
},
"expected": "MMM"
}
]
}
=end code``````
``````unit module RomanNumerals:ver<3>;

sub to-roman (\$number is copy --> Str:D) is export {
my @glyphs = (
:1000M,
:900CM,
:500D,
:400CD,
:100C,
:90XC,
:50L,
:40XL,
:10X,
:9IX,
:5V,
:4IV,
:1I,
);
my \$roman = '';
for @glyphs -> \$p {
while \$number >= \$p.value {
\$roman ~= \$p.key;
\$number -= \$p.value;
}
}
return \$roman;
}``````