12 ms·

To be fair, most of these classes come with "laws" instances are supposed to follow, which are not encoded in the language...

• eru 12y ago
  Good point!
• Fixnum 12y ago
  On the other hand, the burden of proof is on the library writer who creates the typeclass instance, not on the end user - possible largely thanks to purity - whereas programmers may expect to re-implement various patterns by hand.