Array.prototype.filter-like method call expanded into an efficient loop

macroFilter.sjs

macro replace {
	case { _ $a:expr $b:expr { $first $rest ... } } => {
		if ($a.token.value === $first.token.value) {
			return #{ $b replace $a $b $rest ... }
		} else {
			return #{ $first replace $a $b { $rest ... } }
		}
	}
	case { _ $a:expr $b:expr { } } => {
		return [];
	}
}
macro macroFilter {
	case { _($what:expr, function($arg) { $how ... }) } => {
		letstx $return = [makeIdent("return", #{$how ...}[0])];
		return #{
			(function() {
				let $return = macro {
					rule { $result:expr } => { 
						if ($result) results.push(cached[i])
						continue
					}
				}
				let $arg = macro {
					rule {} => { cached[i] }
				}
				var results = [];
				var cached = $what;
				for (var i = 0, len = cached.length; i < len; i++) {
					$how ...
				}
				return results;
			})();
		}
	}
}

macro .mfilter {
	rule infix { $w:expr | ( function($a) { $how ... } ) } => {
		macroFilter($w, function($a) { $how ... })
	}
}

[1, 2, 3].mfilter(function(item) {
	if (something) {
		return false;
	}
	item = item + func(item + 2);
	return !item;
})

(function () {
    var results$430 = [];
    var cached$431 = [
            1,
            2,
            3
        ];
    for (var i$432 = 0, len$433 = cached$431.length; i$432 < len$433; i$432++) {
        if (something) {
            if (false)
                results$430.push(cached$431[i$432]);
            continue;
        }
        cached$431[i$432] = cached$431[i$432] + func(cached$431[i$432] + 2);
        if (!cached$431[i$432])
            results$430.push(cached$431[i$432]);
        continue;
    }
    return results$430;
}());