Opportunities multiply as they are seized. The more computational models you get under your belt the broader your horizon will be. And since the computational model of Haskell is quite unique, you will almost certainly learn more than just new syntax. The same would be true for (e.g.) Prolog, whose computational model is non-mainstream as well. That difference means, you can't understand this new thing in terms of what you knew before, but you need to grok new concepts (not just syntax). As the adage says: “If you know exactly what you're doing, you're not learning anything”.