Presenting - GHC Language Extensions

Slides: link

I gave a presentation a little over a week ago on GHC lkanguage extensions. This blog post is both a publication of the materials and a touch of additional commentary. The presentation was a put together quickly and was meant to explore GHC/Haskell language extensions: what they are, what they do, how they’re used. It goes more for broad coverage rather than precise details. As a result, particularly when reviewing extensions like GADTs or Existential Quantification, the materials are sparse.

Thankfully, the GHC 7.10 User Guide is far more thorough than I. :)

As I read through the user guide, it got me thinking about the base Haskell language, specifically, Haskell 2010. That’s already a rather rich language. Excluding the standard library, and focusing strictly on the language, it features things like:

• Pattern matching
• Conditional matching using if/then/else or guards
• Automatic currying
• A module system
  • Qualified imports (import qualified X.Y as XY)
  • Restricted imports (import X.Y (cat, otherCat))
  • Exclusionary imports (import X.Y hiding (notThatCat))
• Sections: (+1) -- same as (\x -> x + 1)
• Tuples
• Rich type system
  • Pervasive type inference
  • Polymorphic types: Maybe a
  • Higher-kinded types: Either a b -- with kind Either :: * -> * -> *
  • Type constraints and open interfaces, ala typeclasses
  • Generative types ala newtype Age = Age Int
  • Type synonyms ala type Pred a = (a -> Bool)
  • Type definitions allowing for sums, products, and recursion
  • Record types: data Person = Person {name :: String, ...}
• Sugar
  • List comprehensions
  • Do-notation

Given that as a base, it’s interesting to think about how the language extensions might have come about. There’s an extension for (I think) every Haskell 2010 core language feature.

Without further commentary, here’s the slides).

I hope they’re helpful to you, too. It was enlightening spending some time reading through the GHC User Guide to put that together.