The list there you have roughly corresponds to my intuitions, except for a few minor things:

1. Functional dependencies. --- I personally have used functional dependencies and wrestled with things like the coverage condition, and while I know I could easily look it up and would have no trouble understanding it, I doubt I could tell you what each of those is without looking it up. But I've never felt that knowing that is really worthwhile - they're just things the compiler will complain about if I run into them accidentally, and most programmers who have written enough of their own instances probably get them right anyways. So I'm not really sure that understanding those is necessary for being productive on a day-to-day basis, and they seem a bit out of place on that list. Do you have a particular reason they're there?

2. Arrows -- I've been programming Haskell for a few years now, and only run in to arrows in practice a few times. I've definitely seen a few libraries migrating away from arrows towards applicative or monadic interfaces instead. Do you use them often? I definitely feel like they're a bit more on the esoteric side, while GADTs, free monads, lenses, type families, and existential data types are things I encounter fairly frequently. On the other hand, they seem to be a good model for FRP and such, so maybe not. (Same goes for church encodings, but that's just a nice bit of CS that people should know a bit :) )

On the whole, looks like a pretty good list that I agree with. Of course, the "basic" list really includes a bunch more - knowledge of data types, syntax, functions, laziness, etc.

-- Andrew



On Thu, Jul 24, 2014 at 4:01 PM, Wojciech Danilo <wojciech.danilo@gmail.com> wrote:
This is **very** interesting question! 
When we recruit people to our company (we are working in Haskell everyday), we are basing on some classification between basic, intermediate and advanced stuff. These sections are shown below. I would love to hear what others are thinking about it and what from the below stuff would be widely considered as "basic Haskell knowledge", which would allow for full-time basic Haskell work.

Basics

  1. type classes
  2. instances
  3. functors, applicatives, monads, etc (http://www.haskell.org/haskellwiki/Typeclassopedia)
  4. functional dependencies
    1. Patterson condition
    2. Coverage condition
    3. Liberal coverage condition
  5. monad transformers

Intermidiate

  1. lens
  2. arrows
  3. free monads
  4. GADTs
  5. Type families
    1. closed type families
  6. existential datatypes
  7. RankNTypes
  8. church encoding

Advanced

  1. templateHaskell
  2. generics
  3. continuations
  4. delimited continuations


2014-07-25 0:44 GMT+02:00 Johan Larson <johan.g.larson@gmail.com>:

What does a programmer need to know to be proficient in "basic Haskell"?

For my money, basic programming skills are those that are required to
write programs for simple tasks in the common idioms of the language.
This means the practitioner should be able to read input from the
terminal or files, select/combine/reformat data, and output a result.
At this point, efficiency isn't really the point; only getting to a
correct answer without writing anything really weird matters.

In LYAH, I'd put the boundary at the end of chapter 9, which covers
the IO monad. At that point the reader has studied functions, lists,
tuples, types, recursion, higher order functions, four major modules,
and algebraic data types. Actually, some of the later topics in
chapter 8 (functors, kinds, recursive data structures) seem more like
intermediate material.

Thoughts?

--
Johan Larson -- Toronto, Canada
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