The melodic minor scale is the same as the natural minor with the exception that the sixth and seventh tones are raised by a semitone (half step) when the scale is ascending. When the scale is descending, the melodic minor is the same as the natural minor, e.g.:
C, D, E-flat, F, G, A, B, C (ascending)
CThe harmonic minor scale
The harmonic minor scale has just one tonally effective mode and that is the scale conventionally known as the harmonic minor scale. It is spelled, in numerical form (relative to the major scale):

1 2 3 4 5 6 7 Notes
, B-flat, A-flat, G, F, E-flat, D, C (descending)
Greg Stephens.you and your friends are using incorrect terminology,as I stated the tunes you call minor are in fact in the dorian mode .Checkout Junior crehans hornpipes[modern compositions,they are in modes other than major]
Clockwatcher.there are loads of tunes that are not exclusively in the major key,they are mixolydian,Dorian, aeolian,and sometimes mixtures of major and others.