ps: Here's an approximate break-down of the most popular version constraints (normalized via Distribution.Version.simplifyVersionRange) found in the current versions the registered hackage packages (currently 3269 packages): 1004 ==4.* 475 >=3 && <5 439 -any 319 no base dependancy 233 <5 57 >=4 46 >=4.0 && <5 45 >=2 && <5 41 >=3 41 ==3.* 39 >=4.2 && <5 29 >=4 && <4.4 28 >3 && <5 26 >=4.0 && <5.0 26 >3 21 >4 && <5 21 <4 21 >=3 && <=5 19 >=4 && <6 18 >=4 && <=5 17 ==4.3.* 17 >=3.0 17 >=2 && <4 16 >=4.0 && <4.4 14 >=4.3 && <5 13 >=3.0 && <5 12 >=4.2 && <4.4 11 >=3 && <4.4 11 >=2.0 10 >=4.1 && <5 10 >=3.0 && <4.1 9 >=3 && <6 [...tail...]