if not modules then modules = { } end modules ['l-boolean'] = {
    version   = 1.001,
    comment   = "companion to luat-lib.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

boolean = boolean or { }

local type, tonumber = type, tonumber

function boolean.tonumber(b)
    if b then return 1 else return 0 end
end

function toboolean(str,tolerant)
    if tolerant then
        local tstr = type(str)
        if tstr == "string" then
            return str == "true" or str == "yes" or str == "on" or str == "1" or str == "t"
        elseif tstr == "number" then
            return tonumber(str) ~= 0
        elseif tstr == "nil" then
            return false
        else
            return str
        end
    elseif str == "true" then
        return true
    elseif str == "false" then
        return false
    else
        return str
    end
end

function string.is_boolean(str)
    if type(str) == "string" then
        if str == "true" or str == "yes" or str == "on" or str == "t" then
            return true
        elseif str == "false" or str == "no" or str == "off" or str == "f" then
            return false
        end
    end
    return nil
end

function boolean.alwaystrue()
    return true
end

function boolean.falsetrue()
    return false
end