[Haskell-cafe] Haskell's "historical futurism" needs better writing, not better tools

Gregory Guthrie guthrie at miu.edu
Thu Sep 16 15:28:16 UTC 2021

Educational research and learning theory shows that learning anything new is more effective and longer retained when it is connected to and builds on prior knowledge.

People may understand anything new if presented as a completely new set of ideas or principles, but that knowledge is not persistent or long remembered.

I personally find Haskell a good example of this. When teaching it one can show incrementally how it is the same in many ways as procedural programming languages. Then how it improves on them with first-class functions, currying, immutability, type abstractions, etc. These are all important ideas that they will also see in other IP languages, just much cleaner and more integrated in Haskell(!).

Basic Haskell programs with these features can then be used as a bisis for both appreciating the language features and design and FP in general, and as a stepping stone to more advanced usages.

Then introducing Functors, Monads, .... Are again an easy and well motivated step for improving on their existing IP experience, and show both nice abstractions and ideas, and a nice implementation and results.

All of this connects to and builds on what they already know.

Moving into all of the fancier type system features and pragmas, one enters into a realm where Haskell programs are no longer simple enough to easily read as they incorporate several levels of new abstractions and syntax.

But at least students have a good basis for further exploration, and an appreciation of FP and Haskell. :-)

From: Haskell-Cafe <haskell-cafe-bounces at haskell.org> On Behalf Of Richard Eisenberg
Sent: Thursday, September 16, 2021 10:05 AM
To: Anthony Clayden <anthony.d.clayden at gmail.com>
Cc: haskell-cafe at haskell.org
Subject: Re: [Haskell-cafe] Haskell's "historical futurism" needs better writing, not better tools

I just want to pipe up and say I'm not comfortable with this response. When I feel this way about writing on a forum, I normally contact the author in private, but I think posting publicly here has its merits. I'm hoping that the long correspondence AntC and I have had -- often with opposing viewpoints but with mutual respect -- with withstand this email.

Michael posted here expressing frustration with his experience learning and using Haskell. In my opinion, he has spent too much time reading older papers, written by experts for experts -- which Michael is not. I do not fault Michael for this: these resources are sometimes what appear when searching, and we as a community have done a poor job marshaling our educational resources. (Michael, I just thought of a resource you might find useful: http://dev.stephendiehl.com/hask/ is an oft-linked resource attempting to do that marshaling. I am not vouching for it here, per se, but I know others have found it useful.)

However, Michael very specifically said that "just learn lambda-calculus" was not helpful for him, and so I think it's unhelpful for someone to respond with "just learn lambda-calculus". There are a number of other statements in the email below which could be seen as belittling -- also not helpful.

Instead, I wish that we, as a community, could take posts like Michael's at face value: this is the experience of someone who wants to learn Haskell. While some of the conclusions stated in that post are misunderstandings, it is not the sole fault of the learner for these misunderstandings: instead, we must try to understand what about our community and posted materials induced these misunderstandings, and then seek to improve. Many people in Michael's situation may not have posted at all -- and so this kind of information can be very hard to get.

Michael, I have no silver bullet to offer to you to try to help you here. I do tend to agree with AntC that you have developed some misconceptions that are hindering your continued learning. The terminology actively hurts here. (To be fair, the first Haskell standard pre-dates both Java and C++, and so one could argue who got the terms wrong.) For my part, I am trying to help with this situation both by trying to improve error messages, and though my support of the Haskell Foundation's Haskell School initiative (https://github.com/haskellfoundation/HaskellSchool). These will take time to grow, but my hope is that a future person like you will have an easier route in.

In the meantime, I implore us to take all expressed experiences as exactly that: the experience of the person writing. And if they say they don't want X, please let's not feed them X. :)


On Sep 16, 2021, at 12:53 AM, Anthony Clayden <anthony.d.clayden at gmail.com<mailto:anthony.d.clayden at gmail.com>> wrote:

Hi Michael, oh dear, oh dear, oh dear.

The seeds of your confusion are very evident from your message. How to back you out of whatever deep rabbit-hole you've managed to get your head into?

>  ... Your average reader (already a programmer) would be better served by a comparative approach: Here's how to say something in a couple of other programming languages, here's how to say something roughly equivalent in Haskell -- BUT, here's how it's subtly different in Haskell.

No. Just no. Haskell is not "subtly different" to (say) Java in the way that C++ or C# are different. (I'll leave others to judge how subtly different they are.)

Haskell is dramatically and fundamentally different. You can't just 'translate' an algorithm from OOP to Haskell. Many newbies try, and there's many tales of woe on StackOverflow. Just No.

I really don't know how you could have got any experience with Haskell and say "subtly".

I suggest you unlearn everything you think you know about Haskell, and strike out in an entirely different direction. The best approach would be to spend a few days playing with lambda calculus. (That's what I did before tackling Haskell.)

> (I've actually been curtly informed on the beginners' list -- yes, the beginner' list! -- that my problems of comprehension can be solved simply: "Learn lambda calculus.")

Lambda calculus is an excellent place for beginners to start. What could be easier to learn? It's certainly easier than grokking a Turing machine; and much easier than Haskell: less than a handful of primitives yet can compute anything computable.

> And since the concepts are seldom described in concrete enough and time-honored programming language terms (by comparison to other programming languages)

I'm guessing that the concepts you're talking of simply don't correspond to anything in time-honoured (procedural) programming. Anybody writing about Haskell (including anybody writing the User Guide) assumes a base level of understanding of Haskell. You've clearly veered off the track and haven't yet reached base. Remember the User Guide builds on top of the Language Report.

(On the point of 'time-honoured': lambda calculus is almost exactly the same age as Turing machines. The first well-known programming language using lambda-calculus ideas (LISP 1966) is almost exactly the same age as the first OOP language (Simula 1967). Which is the more time-honoured?)

You do have a point that the terminology in Haskell is often mysterious

> [SPJ said] F# had settled on the term "workflow" instead of "monad", and he felt this was wise.

Yes many have yearned for a more warm-and-cuddly term than "monad". But the terminology barrier starts before that.

Haskell typeclasses are not 'classes' in any sense recognisable from OOP. There are no objects, no hidden state, no destructive assignment. We might go back to February 1988 when a strawman for what became typeclasses used OVERLOAD/INSTANCE.


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