Slides and examples from Applicative workshop LambdaConf Winter Retreat, January 2017

Talk Outline:

Monad!

• context dependency: earlier failures can short-circuit later code
• maybe.hs
• either.hs for comparison (this was mostly added after the talk, for the Austin meetup)

Applicative

• another type of functor, different from Functor or Monad
• anagramMaybe.hs
• compare monadic and applicative versions

AccValidation

• datatype from validation library
• anagramEither.hs
• like Either but can accumulate error messages on the left
• acc project

ApplicativeDo

• new language extension lets you use do syntax with applicatives
• see applicDo.hs within acc project

We didn't talk much about parsing but probably should have

optparse-applicative

• library for command line argument parsing
• most of it is implemented applicatively (not monadically, though monadic parsing is also fun)
• we didn't talk about how most of the functions and types this library provides works
• walked through example optex project

using optparse in a project

• command line address book along the lines of ppl addressbook
• this is just the argument parsing portion
• address project