Haskell is, in fact, a really good way to write parser code. That's the main thing I use Haskell for.
But how are you suggesting that Haskell could solve the problem of letting CoffeeScript plugins express which text they should apply to in a CoffeeScript text editor?
He's suggesting that the correct solution (recursive descent parser) is not inherently hard, but CoffeeScript makes it hard enough that people reach for less good approaches.
But how are you suggesting that Haskell could solve the problem of letting CoffeeScript plugins express which text they should apply to in a CoffeeScript text editor?