Having done Clojure for a living before Haskell, it&#x27;s the type system, explicit effects, laziness, overall good design, and FP. In that order.<p>But the &quot;FP&quot; part is only tangentially the point unless you take FP to mean &quot;pure functional programming&quot;, ie, just a lambda calculus.<p>Having the ability to write &quot;map&quot; and &quot;filter&quot; in your programming language doesn&#x27;t really do much for you in practice. Believing otherwise is why people thought FP users were nuts for a long time.