where-macro.js

syntax where = function(ctx) {
  const binaryOps = ["or", "and", "==", ">", "<", "-", "+", "*", "/", "."];
  const dummy = #`dummy`.get(0);

  function matchNext(names) {
    const marker = ctx.mark();
    const next = ctx.next();
    ctx.reset(marker);
    return !next.done && names.includes(next.value.val());
  }

  function readBinaryOp(op) {
    const precIdx = binaryOps.indexOf(op);
    const isLast = precIdx === binaryOps.length - 1;
    const readNext = () => {
      if(isLast) {
        return dummy.fromString("" + ctx.next().value.val());
      }
      return readBinaryOp(binaryOps[precIdx + 1]);
    }
    const left = readNext();

    while(matchNext([op])) {
      ctx.next();
      const right = readNext();
      left = #`({ op: ${dummy.fromString(op)}, left: ${left}, right: ${right} })`;
    }

    return left;
  }

  function read() {
    return readBinaryOp(binaryOps[0]);
  }

  return read();
}

where t.x == 3 / 4 * 2 and z > 10;

// Output:
//
// ({
//     op: "and",
//     left: {
//         op: "==",
//         left: {
//             op: ".",
//             left: "t",
//             right: "x"
//         },
//         right: {
//             op: "*",
//             left: {
//                 op: "/",
//                 left: "3",
//                 right: "4"
//             },
//             right: "2"
//         }
//     },
//     right: {
//         op: ">",
//         left: "z",
//         right: "10"
//     }
// });