[Haskell-cafe] Investing in languages (Was: What isyourfavouriteHaskell "aha" moment?)

Paul aquagnu at gmail.com
Sun Jul 15 16:06:58 UTC 2018

➢ Eta does. Through a very nice FFI. But so does Haskell. We have nice FFI to use C libs. I maintain a couple of libs that use it extensively, works quite well.

I asked because never tried Eta. So, if you are right, seems no reasons to develop Eta...

➢ Can I have a definition and laws of "monad++"? Otherwise, I don't understand what you are talking about. If it obeys monadic laws it is a monad. But I'll wait for the definition. 

No better definition then original: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/computation-expressions  You see, they are different.

➢ But it is not lazy - one. Remember, laziness is our requirement here. Whatever you propose _must _ work in a context of laziness.

Does it mean because Haskell is lazy (Clean – not) then linear types are impossible in Haskell? If they are possible why we need monads? 

➢ Second, the inability to track side effects in F# is not "simplification" and is not a benefit, but rather a limitation and a disadvantage of the language and its type system.

Haskell “tracks” effects obviously. But I shown example with State monad already. As I saw, nobody understand that State monad does not solve problem of spaghetti-code style manipulation with global state. Even more, it masks problem. But it was solved in OOP when all changes of state happen in one place under FSM control (with explicit rules of denied transitions: instead of change you have a request to change/a message, which can fail if transition is denied). Haskell HAS mutable structures, side-effects and allows spaghetti-code.  But magical word “monad” allows to forget about problem and the real solution and to lie that no such problem at whole (it automatically solved due to magical safety of Haskell). Sure, you can do it in Haskell too, but Haskell does not force you, but Smalltalk, for example, forces you.

We often repeat this: “side-effects”, “tracks”, “safe”. But what does it actually mean? Can I have side-effects in Haskell? Yes. Can I mix side-effects? Yes. But in more difficult way than in ML or F#, for example. What is the benefit? Actually no any benefit, it’s easy understandable with simple experiment: if I have a big D program and I remove all “pure” keywords, will it become automatically buggy? No. If I stop to use “pure” totally, will it become buggy? No. If I add “print” for debug purpose in some subroutines, will they become buggy? No. If I mix read/write effects in my subroutine, will it make it buggy? No.

IMHO there is some substitution of concepts. Monads roots are not safety, but workaround to have effects in pure lambdas. And after monads introduction, a thesis was appeared: “monads make code more safe”. Motivation of monads was not to track effect (because it’s allegedly more safe), but to inject/allow/introduce effects in language like Haskell. Good example is State monad, again. State monad is needed to support manipulation of state (through argument replacement in chain of lambdas) but it’s totally other thing in comparison with idea to separate state manipulation in one isolated place under control of some FSM with explicit rules of allowed and denied transitions. If I am switching from read monad to RWST monad, will my code be more buggy? Again, no. Monads don’t decrease buggy or global-state-manipulation problems automatically, they are workaround for specific Haskell problem. Other languages don’t need monads. I CAN have monads in Python, Javascript but I don’t need them. My point is: monads are not valuable byself: Ocaml has not any monads and all is fine 😊

But it’s really very philosophical question, I think that monads are over-hyped actually. I stopped seeing the value of monads by themselves.

➢ Third, AFAIK CLR restrictions do not allow implementing things like Functor, Monad, etc. in F# directly because they can't support HKT. So they workaround the problem.

https://fsprojects.github.io/FSharpPlus/abstractions.html (btw, you can see that monad is monoid here 😉)

➢ But again, F# cannot be expressive enough: no HKT, no ability to express constraints, no ability to track effects...

If F# has monads (you call “monads” to computational expressions), then it CAN...
About HKT: yes, that’s true. But may be, it’s not so big problem? May be you can write effective, good and expressive code without them? Otherwise, we should agree that all languages without HKT are not expressive...

➢ Really?  You keep mentioning F#, and I struggle with it right now _because_ of such limitations. There are no meaningful ways abstract over generics, it is impossible to reason about functions' behaviours from their type signatures (because side effects can happen anywhere), it has Option, but you still can get Null, you can't have constraints, etc., etc. It is sooooo muuuuch mooore limited.

IMHO fear of “side effects can happen anywhere” becomes traditional thesis. And what is the problem if I add “print” in some function?! 😊 Again, substitution of concepts, of monad’s motivations. Haskell compiler can not transform code with side-effects in effective way, and I must isolate all side-effects, mark such functions, but this is the problem of Haskell compiler, not mine. Why programmer should help compiler?! You can look at MLTon compiler, or OCaml one. IMHO they are good and work fine with side-effects; programs WITH side-effects under RWST or State or without those monads in ML are equal: if I port 101 ML functions with side-effects to Haskell, then I will add monad and will have 101 functions with the same side-effects, but now under monad. I can propagate my monad anywhere 😊 All my functions can be under RWST or State. Again, this problem should be solved in other way, not by wrapping the same actions in some wrapper-type (monad). A funny consequence of this, now my program become deep nested lambdas. Compiler should try to “flat” some of them, but I am not competent how Haskell good in it. Anyway, performance will be worse than in ML version. But focus here is a mark-with-monad-type, not the avoid side-effects. And it’s needed for compiler, not for me. May be I’m not clean, may be it is heavy to accept to the people hypnotized by magic invocations about monads power, may be I don’t understand something 😊

➢ No, you can't. 

Something like this:   user?.Phone?.Company?.Name??"missing";     ?

   u <- mbUser
   ph <- phoneOf u
   ...) <|> pure “missing”

➢ OCaml exists for 22 years now, doing well and solves problems it has been designed for very well. So _already_ more than twice compare to your prediction.

It’s Ocaml. It follows to the golden middle, to avoid danger corner 😉

➢ fields are not starting with “_” prefix, so I need to create lenses explicitly
➢ No you don't. You don't have to have "_" prefix to generate a lense. You have total control here. 

Hmm, may be I’m not right. I’m using microlenses and call `makeLensesFor`...

➢ Can you define "business value" please? You mention it for a couple of times, so I am puzzled. Otherwise, it reminds me of https://twitter.com/newhoggy/status/999930802589724672
➢ For Haskell programmers, Java solves non-existing problems all the time :) Every single time you see on twitter or here something like "I replaced hundreds of lines of Java code with a single 'traverse'" you get the proof. And it happens so often.

It involves a long talk 😉 Business value - I’ll illustrate it, imagine a code:

.... lift ....   – NO business value in lift! It’s infrastructure code
m <- loadModel “mymodel.bin” – there is business value
checkModel m rules – there is business value too

So, I can mark infrastructure code with red color, business code with green and to calculate ratio. And to talk about “usefulness/effectivity” of language. How many infrastructure noise have the language (Java, btw, IMHO will have bad ratio too). I have a tons of types, JSON to/from instances, - I repeat models which are coded in external 3rd part services. But F# team thinks like me: it’s not enterprise way to do things in such manner and they introduced types providers – it’s only small example. In Haskell I wrote a lot of infrastructure code, different instances, etc, etc. But other languages are more concentrated on business value, on domain, on business logic. I though about DSLs, but DSLs can be antipattern and to lead to other problems...

➢ Haskell code needs help from IDE, types hints, etc. 
➢ Types are written and read by programmers. Java is impossible without IDE.  What is the point here?

Usually it’s difficult to understand for programmers. Most say: Perl looks like sh*t. Just look at these %, $, etc. And they don’t understand simple thesis: language is about humans, about linguistic, not about computation. Language should not be oriented to compiler or to its computational model, how will you like to work with bytes and words only in C++? So, we have “a”, “the” in English, we have “%”, “$” in Perl. And I don’t know exact object “type” but I can imagine its nature, it’s scalar, vector, etc. In Haskell I can skip most signatures and such code is not readable, I need Intero help to check some types. It’s very bad situation. It’s not 100% true for Java because you will have signatures in Java, you can not skip them, right? And if I add operators noise also (when I have not idea what does this ASCII-art do), the code becomes IDE-centric.

➢ Better for whom? Definitely NOT better for me and my team using Haskell commercially. Again, to effectively meet requirements, functional and non-functional, we don't want just a mediocre compromise thing. I gave you an example with parsers already: different parsers have different tradeoffs. It is often a GOOD thing that there are many different libraries doing the same thing differently. 

Hm, if I have several libraries which are  doing similar things (only due to dependencies), then I have: 1) big Haskell installation (1Gb?) 2) slow compilation 3) big binaries, etc. I understand, you have freedom of choice. But let’s look to IT: C++ turned to one library (imported some Boost solutions, etc, etc), the same R7RS, D with its Phobos, Ocaml has batteries from Jane str., Python 😊 IMHO its general trend. Let’s imagine: project with 2, 3 parsers libraries, conduit and pipes, etc, due to dependencies. So, IMHO my point is not so strange or weird 😉 I’m talking about drop off those libraries (parsers, etc), but about creating of one solid library which components will depends only on it. Other alternatives will be somewhere in repos, who want, can use them without any problems. Something like Qt, Boost, Gtk, etc.

Let me be more precise, I’m comfort with Haskell at whole, but 1) I discussed Haskell with other people 2) I read opinion of other people in industry 2) I’m programmer since 97 and I have critical kind of the mind, so all of these allows me also to look from another POV. And I have been see how it’s similar to the fate of other languages which had good elegant ideas, they followed to one concept, abstraction only. This is the way to be marginalized, what happens with a lot of them. Actually, Haskell is already marginal: you can check how many programmers use it in the world, in most statistics it will not exist even. OK, I’m geek, in real life too, but IT industry is not a geek 😊

/Best regards

On Sun, Jul 15, 2018 at 1:28 AM Paul <aquagnu at gmail.com> wrote:
Hello Alex!
> A small disclaimer: none of the members of our team has an academic background. We all have different backgrounds: C#, Java, Ruby, Python, C, even Perl if I am not mistaken. Yet we ended up with FP first, and then with Haskell.
> We have switched to Haskell from Scala, which _is_ a multi-paradigm language borrowing bits and pieces from other languages/paradigms and mixing them together. It is an enormously hard work to do it and for that, I very much respect 
Oh, my 1st question will be: did you try Eta, Frege? May be I’m wrong but Eta should support Haskell libraries as well as Java ones? They allow you to use libraries from the both world...
> As a result, the language becomes overly complicated and less useful.
Yes, this is another side. You know, anything has several sides: good and bad...
> Your joke about how Haskell has been made misses one point: it was initially designed as a lazy language (at least as far as I know). Many features that Haskell has now are there because of laziness: if you want to be lazy, then you have to be pure, you have to sequence your effects, etc.
True. Laziness makes Haskell unique. I think Haskell makes laziness so popular in modern languages although it was known long ago (as data in “infinite streams”, etc). I think, Miranda was lazy, so Haskell is lazy too 😊 And IMHO there was some lazy dialect of ML (may be, I’m not right).
> "Let's defer lambda, name it IO and let's call it Monad" -  this bit isn't even funny. Monad isn't IO. IO happens to be a monad (as many things do, List as an example), but monad isn't IO and has nothing to do with IO. A horse is classified as Mammal, but Mammal doesn't mean horse _at all_.
Sure. I mean, the need of side-effects (and firstly I/O) led to the monads.
> In a context of a lazy language, you need to sequence your effects (including side effects), that's the first point. The second is that instead of disappearing from Haskell, monads (and other concepts) are making their way to other languages. Scala has them, F# has them, even C# has them (however indirectly). Try to take away List Monad from C# developers and they'll kill you ;)
Better IMHO to have less infrastructure code. Better is to hide all “machinery” in compiler.
My point was that monads are workaround of Haskell problem, this was historically reason of their appearance. And if I have not such limitation in my language I don’t need any monads. What are the monad benefits in ML, for example? They are using in F#, but 1) comp. expressions are not monads but step forward, “monads++” and 2) they play different role in F#: simplifying of the code. And you can avoid them in all languages except Haskell. For example, Prolog can be “pure” and to do I/O without monads, also Clean can as well as F#. Monads have pros, sure, but they are not composable and workaround leads to another workaround – transformers. I’m not unique in my opinion: https://www.youtube.com/watch?v=rvRD_LRaiRs All of this looks like overengineering due to mentioned limitation. No such one in ML, F#. D has keyword “pure”, and didn’t introduce monads. Performance is very important feature of the language, that limitation is the reason #1 why Haskell has bad and unpredictable performance. “do”-block is not the same as “flat” block of C# statements and its performance is not the same. I can achieve Maybe effect with nullable+exceptions or ?-family operators, List with permutations/LINQ, guard with if+break/continue and to do it without sacrificing performance.. ListT/conduits – are just generators/enumerators. Benefit of monads IMHO is small, they are workaround of Haskell problem and are not needed in other languages. Sure, there are monads in Ocaml, Javascript, Python (as experimental libraries), but the reason is hype. Nobody will remember them after 5-10 years... 
Actually this is very-very subjective IMHHHHO 😊
> Lenses and generic lenses help, so be it. But I don't think that anything prevents Haskell from having it, and I don't think that Haskell as a language needs a dramatic change as you depict to make it happen. Just a feature.
When I have legacy code, there are a lot of types which fields are not starting with “_” prefix, so I need to create lenses explicitly... “Infrastructure” code. What is the business value of such code: nothing. For non-Haskell programmer it looks like you try to solve non-existing problem 😊  (very-very provocative point: all Haskell solutions looks very overengineering. The reason is: lambda-abstraction-only. When you try to build something big from little pieces then the process will be very overengineering. Imagine that the pyramids are built of small bricks).
> I don't agree that operators are noise. You certainly can write Haskell almost without operators if you wish.
Here I’m agree with D. Knuth ideas of literature programming: if code can not be easy read and understand on the hard-copy then used language is not fine. Haskell code needs help from IDE, types hints, etc. And I often meet a case when somebody does not understand what monads are in “do” blocks. Also there are a lot of operators in different libraries and no way to know what some operator means (different libraries, even different versions have own set of operators). 
> As for extensions, I think that many more should be just switched on by default.
> You mean that conversion should happen implicitly? Thank you, but no, thank you. This is a source of problems in many languages, and it is such a great thing that Haskell doesn't coerce types implicitly. 
No... Actually, I have not idea what is better. Currently there are a lot of conversions. Some libraries functions expect String, another - Text, also ByteString, lazy/strict, the same with the numbers (word/int/integer). So, conversions happen often.
> I don't understand this "no business value" statement. Value for which business? What does it mean "check types, no business value"? 
There are libraries which nothing do in run-time. Only types playing. Only abstractions over types. And somebody says: oh man, see how many libraries has Haskell. But you can compare libraries of Haskell, Java, C#, Javascript, Perl, Python 😊 All libraries of Java, Python... have business value. Real-world functionality. Not abstract play with types. But more important point is a case with installed Agda 😊 or alternative libraries which does the same/similar things. The reason is important: Haskell moves a lot of functionality to libraries which is not good design IMHO. This is the root of the problem. Better is to have one good solid library bundled with GHC itself (“batteries included”) and only specific things will live in libraries and frameworks. Monads and monads transformers are central thing in Haskell. They a located in libraries. There is standard parser combinators in GHC itself, but you will have in the same project another one (or more than 1!). Etc, etc...
Also installed GHC... Why is it so big!? IMHO it’s time to clear ecosystem, to reduce it to “batteries” 😊
> And then it falls into a famous joke: "The problem with Open Source Software is YOU because YOU are not contributing" :) Meaning that if we want more good libs then we should write more good libs :)
Absolutely true 😊
On Sat, Jul 14, 2018 at 5:05 PM Paul <aquagnu at gmail.com> wrote:
I understand that my points are disputable, sure, example, multi-pardigm Oz – dead 😊 Any rule has exceptions. But my point was that people don’t like elegant and one-abstraction languages. It’s my observation. For me, Smalltalk was good language (mostly dead, except Pharo, which looks cool). Forth – high-level “stack-around-assembler”, mostly dead (Factor looks abandoned, only 8th looks super cool, but it’s not free). What else? Lisp? OK, there are SBCL, Clojure, Racket... But you don’t find even Clojure in languages trends usually. APL, J – super cool! Seems dead (I don’t know what happens with K). ML, SML? By the way, Haskell role was to kill SML community, sure it is sad to acknowledge it, but it’s 100% true...
Haskell try to be minimalistic and IMHO this can lead to death. Joachim, I’m not talking “it’s good/it’s bad”, “multiparadigm is good” or else... I don’t know what is right. It’s my observations only. Looks like it can happen.
If we will look to Haskell history then we see strange curve. I’ll try to describe it with humour, so, please, don;t take it seriously 😊 
•       Let’s be pure lambda fanatics!
•       Is it possible to create a big application?
•       Is it possible to compile and optimize it?!
•       Let’s try...
•       Wow, it’s possible!!! (sure, it’s possible, Lisp did it long-long ago).
•       Looks like puzzle, can be used to write a lot of articles (there were articles about combinators, Jay/Cat/Scheme, etc, now there are a lot of Haskell articles – big interesting in academia. But IMHO academia interest to language can kill it too: Clean, Strongtalk, etc)
•       Stop! How to do I/O? Real programming?!!
•       Ohh, if we will wrap it in lambda and defer it to top level (main::IO ()), it will have I/O type (wrapper is hidden in type)
•       Let’s call it... Monad!!
•       Wow, cool! Works! Anybody should use monads! Does not your language have monads? Then we fly to you! (everybody forgot that monads are workaround of Haskell limitation and are not needed in another languages. Also they lead to low-performance code)
•       But how to compose them???!?!
•       We will wrap/unwrap, wrap/unwrap.. Let’s call it... transformers!!! “Monad transformers” – sounds super cool. Your language does not have “lift” operation, right? Ugh...
•       How to access records fields... How... That’s a question. ‘.’ - no! ‘#’ - no! Eureka! We will add several language extensions and voila!
•       To be continued... 😊
I love Haskell but I think such curve is absolutely impossible in commercial language. With IT managers 😊 To solve problem in a way when solution leads to another problem which needs new solution again and reason is only to keep lambda-abstraction-only (OK, Vanessa, backpacks also 😉) Can you imagine that all cars will have red color? Or any food will be sweet? It’s not technical question, but psychological and linguistic. Why native languages are not so limited? They even borrow words and forms from another one 😊 
Haskell’s core team knows how better then me, and I respect a lot of Haskell users, most of them helped me A LOT (!!!). It’s not opinion even, because I don’t know what is a right way. Let’s call it observation and feeling of the future.
I feel: Haskell has 3 cases: 1) to die 2) to change itself 3) to fork to another language
How I see commercial successful Haskell-like language:
•       No monads, no transformers
•       There are dependent types, linear types
•       There are other evaluation models/abstractions (not only lambda)
•       Special syntax for records fields, etc
•       Less operators noise, language extensions (but it’s very disputable)
•       Solve problems with numerous from/to conversions (strings, etc)
•       Solve problems with libraries
Last point needs explanation:
•       There is a lot of libraries written to check some type concepts only, no any business value. Also there are a lot of libraries written by students while they are learning Haskell: mostly without any business value/abandoned
•       There is situation when you have alternative libraries in one project due to dependencies (but should be one only, not both!)
•       Strange dependencies: I have installed Agda even! Why???!
IMHO problems with libraries and lambda-only-abstraction lead to super slow compilation, big and complex compiler.
So, currently I see (again, it’s my observation only) 2 big “camps”:
1.       Academia, which has own interests, for example, to keep Haskell minimalistic (one-only-abstraction). Trade-off only was to add language extensions but they fragmentizes the language
2.       Practical programmers, which interests are different from 1st “camp”
Another my observation is: a lot of peoples tried Haskell and switched to another languages (C#, F#, etc) because they cannot use it for big enterprise projects (Haskell becomes hobby for small experiments or is dropped off).
Joachim, I’m absolutely agreed that a big company can solve a lot of these problems. But some of them have already own languages (you can compare measure units in Haskell and in F#, what looks better...).
When I said about killer app, I mean: devs like Ruby not due to syntax but RoR. The same Python: sure, Python syntax is very good, but without Zope, Django, TurboGears, SQLAlchemy, Twisted, Tornado, Cheetah, Jinja, etc – nobody will use Python. Sure, there are exceptions: Delphi, CBuilder, for example. But this is bad karma of Borland 😊 They had a lot of compilers (pascal, prolog, c/c++, etc), but... On the other hand after reincarnation we have C# 😊  Actually all these are only observations: nobody knows the future.
/Best regards, Paul
From: Joachim Durchholz
Sent: 13 июля 2018 г. 21:49
To: haskell-cafe at haskell.org
Subject: Re: [Haskell-cafe] Investing in languages (Was: What is yourfavourite Haskell "aha" moment?)
Am 13.07.2018 um 09:38 schrieb PY:
> 1. Haskell limits itself to lambda-only. Example, instead to add other 
> abstractions and to become modern MULTI-paradigm languages,
That's not an interesting property.
"maintainable", "expressive" - THESE are interesting. Multi-paradigm can 
help, but if overdone can hinder it - the earliest multi-paradigm 
language I'm aware of was PL/I, and that was a royal mess I hear.
> So, point #1 is limitation in 
> abstraction: monads, transformers, anything - is function. It's not 
> good.
Actually limiting yourself to a single abstraciton tool can be good. 
This simplifies semantics and makes it easier to build stuff on top of it.
Not that I'm saying that this is necessarily the best thing.
> There were such languages already: Forth, Joy/Cat, APL/J/K... Most of
> them look dead.
Which proves nothing, because many multi-paradigm languages look dead, too.
> When you try to be elegant, your product (language) died.
Proven by Lisp... er, disproven.
> This is not my opinion, this is only my observation. People like 
> diversity and variety: in food, in programming languages, in relations, 
> anywhere :)
Not in programming languages.
Actually multi-paradigm is usually a bad idea. It needs to be done in an 
excellent fashion to create something even remotely usable, while a 
single-paradigm language is much easier to do well.
And in practice, bad language design has much nastier consequences than 
leaving out some desirable feature.
> 2. When language has killer app and killer framework, IMHO it has more 
> chances. But if it has _killer ideas_ only... So, those ideas will be 
> re-implemented in other languages and frameworks but with more simple 
> and typical syntax :)
"Typical" is in the eye of the beholder, so that's another non-argument.
> It's difficult to compete with product, 
> framework, big library, but it's easy to compete with ideas. It's an 
> observation too :-)
Sure, but Haskell has product, framework, big library.
What's missing is commitment by a big company, that's all. Imagine 
Google adopting Haskell, committing to building libraries and looking 
for Haskell programmers in the streets - all of a sudden, Haskell is 
going to be the talk of the day. (Replace "Google" with whatever 
big-name company with deep pockets: Facebook, MS, IBM, you name it.)
> language itself is not argument for me.
You are arguing an awful lot about missing language features 
("multi-paradigm") to credibly make that statement.
> Argument for me (I 
> am usual developer) are killer apps/frameworks/libraries/ecosystem/etc. 
> Currently Haskell has stack only - it's very good, but most languages 
> has similar tools (not all have LTS analogue, but big frameworks are the 
> same).
Yeah, a good library ecosystem is very important, and from the reports I 
see on this list it's not really good enough.
The other issue is that Haskell's extensions make it more difficult to 
have library code interoperate. Though that's a trade-off: The freedom 
to add language features vs. full interoperability. Java opted for the 
other opposite: 100% code interoperability at the cost of a really 
annoying language evolution process, and that gave it a huge library 
But... I'm not going to make the Haskell developers' decisions. If they 
don't feel comfortable with reversing the whole culture and make 
interoperability trump everything else, then I'm not going to blame 
them. I'm not even going to predict anything about Haskell's future, 
because my glass orb is out for repairs and I cannot currently predict 
the future.
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