Hello Erwig

From what I understand, you want a Haskell without typeclasses. Elm [1] would fit that bill nicely.

* Type classes and overloading could be turned off These don't exist in Elm.

* Eq and Show (and maybe Ord) instances would be automatically defined for any data type definition (when type classes are enabled) Eq and Show are implemented by compiler magic, no Ord though.

You could later move the students towards Haskell, after you spoiled them with the Elm compiler messages :-) Cheers, Simon [1] http://elm-lang.org/examples 2017-09-24 3:02 GMT+02:00 erwig :

Dear Haskell aficionados,

We will be using Haskell in an introductory course to computer science for college freshmen. From my past experience in using Haskell for students, the biggest hurdle and source of frustration is the type checker, or more precisely, the error messages generated. I see three major kinds of errors that get in the way of a smoother programming experience:

* Errors resulting from overloading * Errors due to undefined type class instances (specifically, Eq and Show) * Errors in the context of parametric polymorphism

While these problems are not unsurmountable, having to talk about these errors is a distraction from the major goal of explaining basics of (functional) programming. It would be great to have a Haskell compiler that offers the following features (and maybe others):

* Type classes and overloading could be turned off * Eq and Show (and maybe Ord) instances would be automatically defined for any data type definition (when type classes are enabled)

My questions are:

(1) Does there exist a good solution to this problem already?

Should one use Helium? I haven't checked lately, but it used to avoid type classes. This might have the disadvantage of having to switch to GHC in case one wants to use overloading. (I have used Helium in the past, and while I admire the effort, I am not sure it's the best option.)

Are there versions of the Prelude available that accomplish some of this?

(2) Are there other Haskellers out there who also want a simpler, more educationally suited version of GHCi?

(3) If the answer to (1) is NO and to (2) is YES, is there any interest in forming a group for creating something like "EduHaskell"?

I'd be grateful for any comments or suggestions!

Thanks, Martin

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I just have passing commentary on your issues. For the bigger questions at the end of the mail I don't have good answers sadly, although just by convenience on question from SO/reddit/web in general I would stay on GHC/base so they can search their questions. On 23/09/17 22:02, erwig wrote:

* Errors resulting from overloading

On GHC 8.2.1 there is a new flag for `:type +d` which uses type-defaulting for giving non-overloaded versions for functions. Prelude> :type +d foldr foldr :: (a -> b -> b) -> b -> [a] -> b Prelude> :type foldr foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b That help to return some of the convenience from before Foldable was in the Prelude. There also -XTypeApplications which lets you play with the signatures Prelude> :set -XTypeApplications Prelude> import Data.Monoid Prelude> import Data.Set Prelude> :type +v foldMap foldMap :: Foldable t => forall m a. Monoid m => (a -> m) -> t a -> m Prelude> :type foldMap @Set foldMap @Set :: Monoid m => (a -> m) -> Set a -> m Prelude> :type foldMap @Set @(Sum _) foldMap @Set @(Sum _) :: Num w => (a -> Sum w) -> Set a -> Sum w Prelude> :type foldMap @Set @(Sum Int) foldMap @Set @(Sum Int) :: (a -> Sum Int) -> Set a -> Sum Int type +v is to see the explicit forall and thus how the TypeApplications get applied. Lastly there is more help to see what instances are available in the form of link in the haddock pages of the classes.

* Errors due to undefined type class instances (specifically, Eq and Show)

I would teach to define instances for those clases because they are easy to do. They work on types of kind * thus are very down to earth. I remember doing this with LYAH. That way they won't see them as magic and actually understand why the compiler is barfing.

* Errors in the context of parametric polymorphism

Those are actually hard. Classes of working on kinds * -> * are what gives haskell the feeling that the class/instances are hard and magical. Playing with them is the only to get comfortable though. -- -- Ruben -- pgp: 4EE9 28F7 932E F4AD

Dear Martin, Here's the URL for our first lecture: http://cmsc-16100.cs.uchicago.edu/2017/Lectures/01/intro.php It is idiosyncratic, but then, so am I ;-). My experience is that Chicago students love little bits of history that help contextualize what they're learning, and these notes reflect that. We'll be putting up additional lectures as we go. It's pretty easy to find the 2016 version of the class, but it looks like we'll be reworking much of the material. Peace, Stu --------------- Stuart A. Kurtz Professor, Department of Computer Science and the College Director of Undergraduate Studies for Computer Science The University of Chicago

Hi Martin, Helium does support overloading, depending on your choice of flags. If you turn it on, it provides a number of built-in type classes, like Eq and Old. It is just that you cannot define your own classes and instances (work is on the way in this respect). All instances are derived, as you ask. I will be working on extending Helium this (course) year in various directions to make it * suitable as a study object for a course on compiler construction and * adding code generation and type checking for type classes * add import/export facilities (these are currently very straightforward) Helium can be easily installed from Cabal for you to check out and play with. See the website at http://foswiki.cs.uu.nl/foswiki/Helium/WebHome As to your general question on EduHaskell, I’d be interested in such a group, and would like Helium to be that teaching-oriented Haskell compiler. best, Jur

On 24Sep, 2017, at 03:02, erwig wrote:

Dear Haskell aficionados,

We will be using Haskell in an introductory course to computer science for college freshmen. From my past experience in using Haskell for students, the biggest hurdle and source of frustration is the type checker, or more precisely, the error messages generated. I see three major kinds of errors that get in the way of a smoother programming experience:

* Errors resulting from overloading * Errors due to undefined type class instances (specifically, Eq and Show) * Errors in the context of parametric polymorphism

While these problems are not unsurmountable, having to talk about these errors is a distraction from the major goal of explaining basics of (functional) programming. It would be great to have a Haskell compiler that offers the following features (and maybe others):

* Type classes and overloading could be turned off * Eq and Show (and maybe Ord) instances would be automatically defined for any data type definition (when type classes are enabled)

My questions are:

(1) Does there exist a good solution to this problem already?

Should one use Helium? I haven't checked lately, but it used to avoid type classes. This might have the disadvantage of having to switch to GHC in case one wants to use overloading. (I have used Helium in the past, and while I admire the effort, I am not sure it's the best option.)

Are there versions of the Prelude available that accomplish some of this?

(2) Are there other Haskellers out there who also want a simpler, more educationally suited version of GHCi?

(3) If the answer to (1) is NO and to (2) is YES, is there any interest in forming a group for creating something like "EduHaskell"?

I'd be grateful for any comments or suggestions!

Thanks, Martin

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.