My ZuriHac 2023 talk

I gave a talk at Zurihac 2023. Macgyver’s Haskell Compiler: Combinators, Duct Tape, and Two Minutes:

These take a while to load, because each page loads my compiler and then compiles code embedded in the page. See the git repo mentioned during the talk for build instructions.

Eagle-eyed viewers may have noticed localhost:3000 in my browser. This is because I served these files using my hoc tool.

I used the Firenvim browser extension to open Neovim within a slide and then access a terminal to build my compiler.

Many thanks to the organizers of the event. A special thanks to Farhad Mehta for inviting me and for suggesting the title of my talk.

I should have said…​

The slide showing the Church/Scott-encoding of Booleans should have used f g instead of x y, as the variables correspond to different cases and not fields.

I forgot to demo a few things, which is just as well as I was running out of energy towards the end. Perhaps I can show them off in a future talk. Or you can just try them out here.

primes = filterPrime [2..] where
  filterPrime (p:xs) =
    p : filterPrime [x | x <- xs, x `mod` p /= 0]

take 100 primes

Edit the code and run it again by clicking the play button, or by pressing Ctrl+Enter. Alternatively, press Alt+Enter to run the code and create a new text area.

The interpreter accepts expressions along with definitions. Like GHCi, expressions of type IO _ are run; otherwise, if the type has a Show instance, the value is printed.

The espy function prints the combinators produced by my compiler.

Some Scott encodings:

espy True
espy $ Just 'x'
espy foldr

The following is a big mess. We can the dictionary selector has yet to be reduced:

abc = ['a'..'z']
espy abc

Evaluating the first 12 elements of the list cleans up the expression a little, thanks to laziness:

take 12 abc
espy abc

Full reduction leads to the normal form:

abc
espy abc

Another example. The * means itself. Again, we have unevaluated dictionary selectors.

fac n = if 1 < n then n * fac (n - 1) else 1 :: Int
espy fac

Much better:

fac 1
espy fac

Without the Int annotation, the fac function is polymorphic and hence more verbose because it can always handle any Ring instance.

Ben Lynn blynn@cs.stanford.edu 💡