lens over tea

A series of articles (called “lens over tea”) about lens and its implementation.

• part 1 – lenses 101, traversals 101, a bit of implementation details (also lens operators, functor composition, Const, Identity, difference lists, monoids of endomorphisms under composition, default signatures for class methods, equality constraints, and irrefutable patterns).

• part 2 – composition, laws, getters/actions/setters (also history of lenses, categories, the way to write lenses which would compose “normally”, some links to Reader/Writer/State learning materials, Void).

• part 3 – folds (also Foldable, Apply, a nice trick for combining folds, and Fold1).

• part 4 – isomorphisms, some profunctors, lens families (also Forget, Tagged, Proxy, a bit about pure profunctor lenses, existential types, algebra of types, and a cat video).

• part 5 – prisms (also a recap of isomorphisms with diagrams, a bit about affine traversals, Pointed, and coerce).

• part 6 – Template Haskell, aka “write your own makeLenses”

It’s a work in progress; the future parts will mention:

• indexed things
• Bazaar/Magma/Molten/Mafic, traversal stuff like partsOf, taking
• fusing and confusing
• benchmarks (view _1 vs fst? how much does fusing help? etc)
• vertical composition, link
• ala, AlongsideLeft
• upon, link
• pure profunctor lenses and traversals, link 1, link 2, link 3, link 4, symmetric lenses ((g a -> f b) -> g s -> f t), link
• Control.Lens.Plated, Control.Lens.Level, Control.Lens.Zoom

Other Haskell stuff

• Aeson: the tutorial
• Making a CTF task in Haskell
• Some common and annoying mistakes in Haddocks

Stuff that is sort of related to psychology

• Unconditional empathy
• The YX problem

Stuff that is sort of related to linguistics

• Why you don’t want “irregardless” to be a word
• Polysemy (i.e. overloading) in programming

Racket

Several years ago I’ve been learning Racket and making notes (which then became somewhat popular):

• Introduction. First three days, no prior knowledge, getting a feel for the syntax… You get the idea.

• Macros, Macros and a Bit of Modules. Another three days. Mostly macros, as you could’ve guessed.