Module:Sandbox/Squc/Roman

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This module converts Roman numerals to decimal form, and rejects invalid ones. It can be used normally, or through another module. This is still under construction, check back in a few days!

This module is intended to run through a template, which is still under construction.

To convert Roman numerals to decimal form, use {{#invoke:Sandbox/Squc/Roman|todecimal|MMXIII}}, which outputs . If the Roman numeral is invalid, it will throw an error. If JavaScript is enabled, you can click the Script error link, and the first sentence should show the cause of the error. The final value will still be given in brackets after the error messages.

To force no errors, use {{#invoke:Sandbox/Squc/Roman|todecimal|MMXIII}}.

To output errors directly into the text, use {{#invoke:Sandbox/Squc/Roman|todecimal|MMXIII}}.

To use this through another module, use something like this:

local roman = require( "Module:Sandbox/Squc/Roman" )

local romannum = "MMXIII"
local value = roman.todecimald( romannum )

Error demonstration

function	No errors	Warnings	Invalid	Errors
Example	MMXIII	XXXXX	XCC	ABC
todecimal
todecimal|mode=1
todecimal|mode=2|disp=Decimal ...
todecimald	Intended for use only from other modules. See below for more details.

Errors will be combined, e.g. "XXXXXXCC" gives:

or with mode=2|disp=0 (default):

todecimald

The function todecimald (direct) is only intended for use in other modules. The output will be in the form (comma-separated list): Decimal, Error message, Time taken

The decimal will be a number, it will be the converted number if there are no errors or if it is a warning (it is invalid but still can be converted), it will be -1 if there is an error (cannot be converted). The error message is a string and will always exist, it will be "" if no error is found.

The above documentation is transcluded from Module:Sandbox/Squc/Roman/doc. (edit | history)
Editors can experiment in this module's sandbox (create | mirror) and testcases (create) pages.
Subpages of this module.

-- Module to convert Roman numerals and reject invalid numerals

local p={}

function p.todecimal( frame )
    local input = frame.args[1]
    local num, err = todec( input )
    if err == nil then
        if num ~= -1 then return num
        else error("Unknown error 3") end
    else
        error(err)
    end
end

local function todec ( rnum )

    if rnum == "" then return -1 , ("Input is empty") end
    if type(rnum) ~= "string" then return -1 , ("Input is not a string") end
    rnum = rnum:upper()
    rnum = rnum:match'^%s*(.*%S)'
    local extra = rnum:gsub("[MDCLXVI]","")
    if #extra ~= 0 then return -1 , ("Extra characters " .. extra .. " found") end
    
    local value = {
        I = 1,
        V = 5,
        X = 10,
        L = 50,
        C = 100,
        D = 500,
        M = 1000
    }
    local symbol = {}
    for i,v in ipairs(value) do symbol[v] = i end -- reverse value table
    local prev, curr, cu1d, run, dec = 0
    local psym, csym = "" -- previous symbol, current symbol
    
    for i = 1, #rnum do
        csym = rnum:sub(i, i)
        local curr = value[symbol]
        cu1d = tostring( value ):sub( 1, 1 )  -- first digit of curr (1 or 5)
        if curr < prev or prev == 0 then
            
            run = 1
            num = num + prev*run
            
        elseif curr == prev then
            
            if cu1d == "1" then
                if run == 4 then                            -- e.g. "XXXXX" for 50, "L" suggested
                    return -1,("More than four " .. csym .. " in a row, suggestion: " .. symbol[ curr*5 ] .. "? - Char " .. tostring(i))
                elseif run == 0 then                        -- e.g. occurs after curr > prev (below) e.g. "XCC"
                    return -1,("Repeat after subtraction - " .. rnum:sub(i-2, i-2) .. psym .. csym .. " - Char " .. tostring(i))
                else
                    run = run + 1
                end
            elseif cu1d == "5" then                         -- e.g. "VV" for 10, "X" suggested
                return -1,(psym .. " cannot be with another ".. csym ..", suggestion: " .. symbol[curr*2] .. "? - Char " .. tostring(i))
            else return -1,("Unknown error 1") end
        
        elseif curr > prev then
            
            if curr > prev * 10 then                        -- e.g. "XM" or "IL"
                return -1,(csym .. " cannot follow " .. psym .. " (Subtraction can only be within the same digit) Char " .. tostring(i))
            elseif tostring( prev ):sub(1, 1) == "5" then   -- e.g. "LC" for 50
                return -1,(csym .. " cannot follow " .. psym .. " (Cannot subtract from " .. tostring(prev) .. ") Char " .. tostring(i))
            elseif run > 2 then                             -- e.g. "XXXL" for 20
                return -1,("Number of" .. psym .. " before " .. csym .. " must be at most two - Char " .. tostring(i))
            else 
                num = num - prev*run + curr
                curr = 0
            end
        
        else return -1,("Unknown error 2") end
        
        prev = curr
        psym = csym
    end
    num = num + prev*run
    return num
end

return p