bind.js

var bind = function(f) {
  return function(tuple) {
    var x  = tuple[0],
        s  = tuple[1],
        fx = f(x),
        y  = fx[0],
        t  = fx[1];

    return [y, s + t];
  };
};

const bind =
  fn => {
    return tuple => {
      // Incoming number and message.
      // E.g. [ 0.5, '(start) ' ]
      let [ inNum, inMsg ] = tuple;

      // Number and message result coming running `fn(inNum)`.
      // E.g. sineWithMsg(0.5)
      // => [ 0.47942, 'sine was called. ' ]
      let [ resNum, resMsg ] = fn(inNum);

      // Output the result number and a concatenated message.
      // E.g. [ 0.47942, '(start) sine was called. ' ]
      return [ resNum, (inMsg + resMsg) ];
    }
  };