What concepts relatively unique to Haskell are powerful, widely applicable, and not mentioned in most introductory texts? (By "relatively unique to Haskell" I mean maybe they're part of Lisp or Scheme, but not, say, Java.)

Some of the concepts important to Haskell, such as lambda expressions and recursion, are also present in more popular languages. Many others, though, either have no equivalent in (most) other languages, or else are very unlike the equivalent:

    types, classes and kinds

    higher-order functions

    evaluation

        partial application

        tail recursion

        laziness

        currying

        pattern matching

        application and composition operations

    contexts

        functors, applicatives, monads

        monad transformers

    lenses

    :def macros

    arrows

    continuation passing style

    software transactional memory

Most of those topics appear to be covered by introductory texts, but the last five are not. I found each of them by accident, and each kind of blew my mind. They all strike me as powerful, widely applicable, and obscure.

Are there others?

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