Converts roman numbers to Int32.

ConvertFrom-RomanNumber.ps1

function ConvertFrom-RomanNumber {
    [CmdletBinding()]
    [OutputType([int])]
    param   (
        #   
        [Parameter(Mandatory,ValueFromPipeline,Position=0)]
        [ValidatePattern('^[ivxlcdmIVXLCDM]+$')]
        [string]$InputObject
    )
    begin   {
        $dictionary     =   @{
            [char]'I'   =   1
            [char]'V'   =   5
            [char]'X'   =   10
            [char]'L'   =   50
            [char]'C'   =   100
            [char]'D'   =   500
            [char]'M'   =   1000
        }
    }
    process {
        $InputObject    =   $InputObject.ToUpper()
        [int]$valueRight    =   $dictionary.Item($InputObject[-1])
        [int]$valueLeft     =   0
        [int]$result        =   0
        if  ($InputObject.Length -eq 1) {
            return $valueRight
        }
        $result +=  $valueRight
        for ($i = $InputObject.Length - 2; $i -ge 0; $i--)  {
            $valueLeft  =   $dictionary.Item($InputObject[$i])
            if  ($valueLeft -lt $valueRight)    {
                $result -=  $valueLeft
            }
            else {
                $result +=  $valueLeft
            }
            $valueRight =   $valueLeft
        }
        return  $result
    }
    end     {}
}

TODO: write reverse converter, from Int32 to roman

Useful article: https://englishhistory.net/romans/roman-numerals/