dart

Haversine formula

```
import 'dart:math';

var R = 6371e3; // earth radius
num degToRad(num deg) => deg * (pi / 180.0);
num radToDeg(num rad) => rad * (180.0 / pi);

/*
Haversine formula

a = sin²(Δφ/2) + cos φ1 ⋅ cos φ2 ⋅ sin²(Δλ/2)
c = 2 ⋅ atan2( √a, √(1−a) )
d = R ⋅ c

*/
double calculateDistance(double lat1, double lng1, double lat2, double lng2) {
  var deltaLat = degToRad(lat2 - lat1);
  var deltaLng = degToRad(lng2 - lng1);

  var a = sin(deltaLat / 2) * sin(deltaLat / 2) +
      cos(degToRad(lat1)) * cos(degToRad(lat2)) *
          sin(deltaLng / 2) *
          sin(deltaLng / 2);

  var c = 2 * atan2(sqrt(a), sqrt(1 - a));
  var d = R * c;
  return d; // returns m
}
```

This part cos(degToRad(lat1) * cos(degToRad(lat2))) * contains an error. The parentheses are not closed correctly.

This part cos(degToRad(lat1) * cos(degToRad(lat2))) * contains an error. The parentheses are not closed correctly.

Good catch man, fixed.