Edit

Roman Numerals

Challenge: Printing and Parsing Roman Numerals

Roman numerals constitute a numeral system capable of expressing positive integers by additive values (rather than place-number notation). Additive series are produced by summing values in a series, as iii → 3, while subtractive values are produced by prepending certain smaller values ahead of a larger value, as ix → 9.

  • Produce a library which converts to and from Roman numeral representations according to the standard values:

    Character
    Value

    i

    1

    v

    5

    x

    10

    l

    50

    c

    100

    d

    500

    m

    1,000

    There are many incorrect formulations, as iix → 8 or id → 499, and the code is not expected to parse these “correctly”. (It should not produce them!) However, both iv and iiii are frequently used to represent 4 (e.g. look at a clock face), so you should support this variation.

    For this task, produce two files:

    • /lib/roman/hoon

      Your library /lib/roman/hoon should expose two arms:

      • +parse accepts a $tape text string containing a Roman numeral expression in lower or upper case and returns the corresponding @ud unsigned decimal value. On failure to parse, call !! zapzap.

      • +yield accepts a @ud unsigned decimal value and returns the corresponding $tape text string in lower case.

    • /gen/roman/hoon

      Provide a %say generator at /gen/roman/hoon which accepts a $tape text string or a @ud unsigned decimal value and performs the appropriate conversion on the basis of the sample's type.

      Note: This design pattern is not optimal since analysis over a union of some types can be difficult to carry out, and it would be better to either separate the generators or use a flag. In this case, the pattern works because we are distinguishing an atom from a cell.

Unit Tests

Following a principle of test-driven development, we compose a series of tests which allow us to rigorously check for expected behavior.

Solutions

These solutions were submitted by the Urbit community as part of a competition in ~2022.6. They are made available under both the MIT license and the CC0 license. We ask you to acknowledge authorship should you utilize these elsewhere.

Solution #1

This solution was produced by ~sidnym-ladrut. This code utilizes the Hoon parser tools like +cook and +scan, and in particular illustrates a strong ethic of function encapsulation.

/lib/roman.hoon

/gen/roman.hoon

Solution #2

This solution was produced by ~mocmex-pollen. It particularly illustrates the use of +cook and +pose in constructing a parser-based solution.

/lib/roman.hoon

/gen/roman.hoon

Solution #3

This solution was produced by ~mashex-masrex. Notice how it utilizes a well-structured parser based on +jest and +cold.

/lib/roman.hoon

/gen/roman.hoon

Solution #4

This solution was produced by ~fonnyx-nopmer. It comes sans comments, and particularly demonstrates how to produce legible and idiomatic Hoon code without requiring comments.

/lib/roman.hoon

/gen/roman.hoon

PreviousRhonda NumbersNextSolitaire Cipher

Last updated