> Imperative programs can have isolated, pure subsections of functionality which are based on composition and immutability. And functional programming language

> Imperative programs can have isolated, pure subsections of functionality which are based on composition and immutability. And functional programming languages can support imperative programming and mutation, even Haskell. It's a question of what should be the default, which depends on the domain you are working in. > Any real banking system has much more than a ledger to deal with. Most banking systems are cobbled together from third-party components and libraries. Low-level languages aren't really needed. Many banks use Python, which is orders of magnitude slower than Haskell. > This comment strikes me as if it comes from someone who never dealt with significant amount of data. Actually I have a background in distributed computing, where functional programming abstractions have made processing large amounts of data much easier (MapReduce, Spark). > FP can be extremely wasteful; take head-tail lists for example, which are the default container in many FPs. This is a strawman. I can write inefficient code in any language. C++ code can be littered with pointer indirection and memory barriers. > Sometimes, arguing with FP purists feels like debating socialists. I am a socialist.