[Haskell-cafe] Looking for feedback on my beginner's Haskell resource

Joachim Durchholz jo at durchholz.org
Sat Nov 3 08:22:59 UTC 2018

Am 03.11.18 um 02:46 schrieb André Popovitch:
> However, 
> I'm not extremely knowledgeable about Haskell and I wouldn't say I'm the 
> best teacher, so if anyone is willing to skim it or provide feedback 
> that would be much appreciated!

One kind of typo that's common enough to become annoying:
comma/fullstop and subsequent space were interchanged.

Well-written overall. I'm pretty sure different people will have 
different ideas about what's important about Haskell, but I think your 
take is valid.
Besides, the knowledgeable people won't know what a newbie will find 
most interesting or enlightening about Haskell, so you'll have to get 
feedback from non-Haskellers to judge how successful that site is.

Some details aren't quite right (as is to be expected with anything that 
goes beyond a dozen pages).

E.g. mutability does increase the number of variables you have to keep 
track of, it multiplies the amount of information you have to keep track 
of for each variable (namely the set of locations where it is changed).

Stating that Haskell does not have side effects will cause cognitive 
Technically, Haskell does not have it, but there's that technique to put 
state into a function that you return, hiding the state not in a 
transparent data object but in a pretty opaque function object. This is 
being systematically (ab?)used in many monads, and in practice, it has 
exactly the same benefit as a mutable global state (you don't have to 
thread it through every function call, it's globally available), and the 
same problems (you don't know where it might be changed).
And then there's IO, which is a different way to do mutability except by 
name. (I have never been able to find out what the concept behind IO is. 
My best guess is that it's a framework to set up descriptions of IO 
interactions, which tend to be infinite which isn't a problem since 
Haskell is lazy, but this may well be totally wrong. SPJ seemingly takes 
this for granted, and all the docs I could find just described the 
mechanics of using it, often with an implicit assumption that IO is a 
magical mutability enclave in Haskell, which I'm pretty sure is not 
actually the case.)
I don't know enough to give good advice how to be neither wrong enough 
to confuse newbies with cognitive dissonance nor correct enough to 
confuse newbies with the full truth.

You should mention that `rem` needs to be typed including backquotes. 
With some fonts, they might look similar enough to normal quotes, and 
then be ignored.
(That point in the presentation might be a good place for a side remark, 
explaining how Haskell allows using operators as functions, and how it 
allows using functions as operators.)

A sidebar notice might help to explain that Haskell's function call 
syntax is nearer to mathematical than programming language conventions: 
Mathematicians write "sin x", not "sin(x)"; they use parentheses only 
when precedences get in the way, e.g. they'll write "(sin x) + 1" if 
needed, or maybe "sin (x + 1)" but the "(x + 1)" isn't function-call 
syntax, it's precedence-altering syntax.
(As conventions go in mathematics, it's just a common one, not a 
universal one. Mathematicians are horribly sloppy about their 
conventions. In fact they are sloppy about anything except the topic 
they're currently interested in. Well, programmers are obsessed about 
irrelevant detail because compilers force them into that habit, from 
their perspective, so both sides are right in a sense ;-)

Okay, enough for now.


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