neongreen/artyom.me

artyom.me's Issues

Mention ALens etc. and ImpredicativeTypes in lens over tea

Switch to make

make cv, make all, etc

Use separate folders for posts, drafts, etc

Remove endnotes from lens-over-tea-2 (or is it 3?)

Switch to HTTPS

https://letsencrypt.org/

Aeson tutorial: add an example of handling lowercase-but-camel fields, and underscored fields

Replace “[RSS]” with an icon

Write a CV

Type signature of `iterated` is incorrect in lens over tea #3

You have

iterated :: Fold1 a a
iterated f g a = go a
  where go a = g a .> go (f a)

but I think it should be

iterated :: (a -> a) -> Fold1 a a
iterated f g a = go a
  where go a = g a .> go (f a)

The signatures in the open question below agree with this.

All the best,
Richard

Make font smaller

Aeson tutorial: improve description of `.:?`

Currently it reads:

.:? is just like .:, but doesn't fail if the field wasn't found (it does fail if the field was found but has a different type, however).

That description actually matches the .:! operator, not .:?.

.:! doesn't fail if the field wasn't found.

.:? doesn't fail if the field wasn't found or if its value is Null.

See the docs for .:?.

This shouldn't usually come up, it can't hurt to be precise. I'm really enjoying the tutorial so far btw!

[artyom.me] and [RSS] collide on mobile

Slightly rewrite the Aeson tutorial

• remove the rant in the beginning
• mention <|> and sum types better

Add lenses to the Aeson tutorial

People are linking to this repo instead of my site

@manpages is the first offender!

Move the recap of isomorphisms into lens-over-tea-4

Embed post content in the feed

lens-over-tea-1: outdated link. Hackage doesn't find Data.Bifunctor inside of bifunctors-5.5

The link in lens-over-tea-1.md

[`second`][] is a function from `Data.Bifunctor`

points to non-existing http://hackage.haskell.org/package/bifunctors-5.5/docs/Data-Bifunctor.html#v:second

Consider to replace it statically by
https://hackage.haskell.org/package/bifunctors-5/docs/Data-Bifunctor.html#v:second

Possibly use jle's thing in lens over tea

02:08 <magbo> (<%~) l h y = l (\x -> (h x, h x)) y 
02:08 <magbo> Works on every lens.
02:08 <magbo> Returns (b, t) -- updated focused value and updated source
02:09 <puregreen> magbo: do you know how the Functor instance for (,) works?
02:09 <magbo> (,) is the outer functor, that was my intention when I was writing it
02:10 <magbo> puregreen: oh snap, it answers my question!
02:10 <jle`> it's Writer! :O
02:11 <jle`> magbo: `(\x -> tell (h x) >> return (h x))` would get you 
             the Writer translation of what you wrote
02:11 <puregreen> jle`: ooh, I like this one
02:12 <puregreen> gotta steal it for lens over tea
02:12 <jle`> it's technically wrong because it requires a Monoid instance i think
02:16 <jle`> puregreen: oh, you can get a working version of what i wrote
             with tell (h x) $> h x, because while it's equivalent to 
             tell (h x) *> return (h x), it doesn't require a Monoid constraint

Isomorphism explanation, enum confusion

Hello,
First of all, thanks for the great series :)

I'm trying to understand the note about enum in lens over tea 4. Specifically, this part:

Now let's consider 2 cases – the first is when we use it to turn s into a, the second is when we use the iso to turn b into t. The definition we already have works well enough for the former case, but in the latter case s doesn't even exist:

enum f = \_ -> fromEnum <$> f ???

I don't understand what you mean by saying "turn the b into the t".

From what I understand,

enum :: Lens' Int a
enum :: Lens Int Int a a ~= Lens s t a b
b -> t :: a -> Int

why is this not a valid candidate?

enum_rev :: Lens' a Int
enum_rev f a = toEnum <$> f (fromEnum a)