Chained comparisons using sweet.js

gistfile1.js

macro $if {
    case ($x ...) => { if (relCar($x ...)) }
}

macro $while {
    case ($x ...) => { while (relCar($x ...)) }
}

// naive form:
/*
macro rel {
    case $x => { $x }
    case ($x:ident $op $y:ident $rest ...) => {
        $x $op $y && $rel($y $rest ...)
    }
}
*/

// better: works even with the presence of &&, |, etc.
macro relGen {
    case ($cmp ...) => {
        macro relCar {
            $(case ($x $cmp $y $rest $[...]) => {
                $x $cmp $y relCdr($y $rest $[...])
            }) ...
            case $x => { $x }
        }

        macro relCdr {
            $(case ($y $cmp $z) => {
                && $y $cmp $z
            }) ...
            /* since the following two sequences are of equal length, order is important */
            case ($y:ident $op $z:ident $rest $[...]) => {
                $op relCar($z $rest $[...])
            }
            $(case ($y:ident $cmp $z:ident $rest $[...]) => {
                && $y $cmp $z relCdr($z $rest $[...])
            }) ...
            case $y => { $y }
        }
    }
}

relGen(>= <= > < != !== === ==)

$while (1 > 2 > 3 >= 4 <= 5 > 6) {
    console.log("foo");
}

$if (1 < 2 < 3 < 4 < 5 < 6) {
    console.log("bar");
}

$if (1 < 2 && 3 < 4 < 5 || 1 == 2 == 3) {
    console.log("bar");
}

// result:
/*
while (1 > 2 && 2 > 3 && 3 >= 4 && 4 <= 5 && 5 > 6) {
    console.log('foo');
}
if (1 < 2 && 2 < 3 && 3 < 4 && 4 < 5 && 5 < 6) {
    console.log('bar');
}
if (1 < 2 && 3 < 4 && 4 < 5 || 1 == 2 && 2 == 3) {
    console.log('bar');
}
*/