AuroraForEach/forEach.js

const fs = require("fs")
const kWantMaxSupportedElements = 100
const kMaxPairedElements = 10
const kMacroParamLimit = 127

function forN(n, cb) {
    for (var i = 0; i < n; i++) {
        cb(i)
    }
}

function genArray(n) {
    return [...Array(n).keys()]
}

function formatNJoin(n, start, join) {
    return start + genArray(n).join(join)
}

function formatNJoinReverseSuffix(n, start, join, suffix) {
    return start + genArray(n).reverse().join(suffix + join) + suffix
}

function formatNParamPattern(n, join) {
    return formatNJoin(n, join, ", " + join)
}

function formatNParamPatternReverseSuffix(n, join, suffix) {
    return formatNJoinReverseSuffix(n, join, ", " + join, suffix)
}

var textBuffer = ""

textBuffer += 
`/**
 * X-Macro alternative. Defines AU_FOR_EACH_N(expandable, ...args*N)
 * Autogenerated by forEach.js; do not modify"
 */

#define AU_FE_EXPAND(exp) exp
#define AU_FE_ERROR(exp) ERROR. CHECK PARAMETER COUNT. DID YOU FORGET A COMMA?
`

forN(kMaxPairedElements, function(nElements) {
    if (!nElements) return
    
    var suffix = nElements != 1 ? "_" + (nElements): ""
    
    var nElementsMulNCapped  = Math.min(kMacroParamLimit - 3, kWantMaxSupportedElements * nElements)
    
    var ignoreList      = {}
    var ignoreListFirst = {}
    
    forN(nElementsMulNCapped, function(i) {
        if (i == 0) {
            textBuffer += `#define AU_FE_0${suffix}(expandable) \n`
            ignoreListFirst[`AU_FE_0_FIRST${suffix}`] = true
            return
        }
        
        var X = formatNParamPattern(nElements, "X")
        var iM1 = i - 1
        var iM1Translated = i - nElements

        if (i == nElements - 1) {
            // Edge case: the trailing macro does not do anything
            // We could hack in an _LAST callback here, should a need for it arise
            textBuffer += `#define AU_FE_${i}${suffix}(expandable)\n`
        } else if ((i == 1) && (nElements != 1)) { 
            // Edge case: FOR_EACH_N(EXPANDABLE, ), where N has to be defined/has an element count of > 1, this is always illegal
            // However, we just ignore empty element expansions 
            textBuffer += `#define AU_FE_${i}${suffix}(expandable, empty)\n`
        } else if (i % nElements == 0) {
            if (i == nElements) {
                // Edge case: the last element does not accept any parameters
                textBuffer += `#define AU_FE_${i}${suffix}(expandable, ${X})               expandable(${X}) AU_FE_EXPAND(AU_FE_${iM1Translated}${suffix}(expandable))\n`
            } else {
                textBuffer += `#define AU_FE_${i}${suffix}(expandable, ${X}, ...)          expandable(${X}) AU_FE_EXPAND(AU_FE_${iM1Translated}${suffix}(expandable, __VA_ARGS__))\n`
            }
        } else {
            ignoreList[`AU_FE_${i}${suffix}`] = true
        }
        
        // Similar to above
        var I2 = i + 1
        if (i == 1) {
            textBuffer += `#define AU_FE_${i}_FIRST${suffix}(first, second) \n`
        } else if (i < nElements) {
            ignoreListFirst[`AU_FE_${i}_FIRST${suffix}`] = true
        } else if ((i % (nElements) == 0)) {
            if (i == nElements) {
                ignoreListFirst[`AU_FE_${i}_FIRST${suffix}`] = true // ? dont question it 
                textBuffer += `#define AU_FE_${I2}_FIRST${suffix}(first, second, ${X})      first(${X}) AU_FE_EXPAND(AU_FE_${iM1Translated}${suffix}(second))\n`
            } else {
                textBuffer += `#define AU_FE_${I2}_FIRST${suffix}(first, second, ${X}, ...) first(${X}) AU_FE_EXPAND(AU_FE_${iM1Translated}${suffix}(second, __VA_ARGS__))\n`
            }  
        } else {
            ignoreListFirst[`AU_FE_${I2}_FIRST${suffix}`] = true
        }
    })
    
    // Defines a macro that effectively choses a macro given an array of macros based on the number of input arguments  
    var getMacroParams = formatNParamPattern(nElementsMulNCapped, "_")
    textBuffer += `#define AU_GET_MACRO${suffix}(${getMacroParams}, NAME,...) NAME\n`
    
    // Stringify the parameter portion of the prototype
    var params  = formatNParamPatternReverseSuffix(nElementsMulNCapped, "AU_FE_", suffix)
    var params2 = formatNParamPatternReverseSuffix(nElementsMulNCapped, "AU_FE_", "_FIRST" + suffix)
    
    // Replace missing macro paramaters with the AU_FE_ERROR macro
    params  = params.split(", ").map((str) => { return ignoreList[str] ? "AU_FE_ERROR" : str}).join(", ")
    params2 = params2.split(", ").map((str) => { return ignoreListFirst[str] ? "AU_FE_ERROR" : str}).join(", ")
    
    textBuffer += `#define AU_FOR_EACH${suffix}(action, ...) AU_FE_EXPAND(AU_GET_MACRO${suffix}(_whydoweneedthis, __VA_ARGS__, ${params})(action,__VA_ARGS__))\n`
    textBuffer += `#define AU_FOR_EACH_FIRST${suffix}(action, ...) AU_FE_EXPAND(AU_GET_MACRO${suffix}(_whydoweneedthis, __VA_ARGS__, ${params2})(action,__VA_ARGS__))`
    
    textBuffer += "\n\n"
})

fs.writeFileSync("./Include/AuroraForEach.hpp", textBuffer)