Prolog. After coding in "normal" (iterative/procedural) languages for a long while, this rule-based languaged just couldn't click. It finally did after about a

Prolog. After coding in "normal" (iterative/procedural) languages for a long while, this rule-based languaged just couldn't click. It finally did after about a week. And bam. Changed my thinking. Also, learn Scheme, or Lisp. You'll rethink recursion after that.