chiroptical

title	description
Abilities in Unison	Unison's type system tracks which functions can do I/O, and the same language feature, called _abilities_ can be used for many other things, too. This is a tutorial on abilities.

Abilities in Unison

Here are two functions in Unison. One performs I/O (it writes to the console) and so it has an interesting type we'll be explaining much more in this tutorial:

chiroptical

all_commands=(
  run
  run.file
  run.pipe
  transcript
  version
  help
  -codebase
  transcript.fork
)

chiroptical

-- These are watchers, they run every time we reload this file in Unison repl
> Stack.run Stack.one
> Stack.run Stack.two
> Stack.run Stack.three

Stack.three : '{Stack List Nat} [Nat]
Stack.three = 'let
  Stack.put 1
  match Stack.pop with
    None -> []

chiroptical

• Update the machine

sudo apt update
sudo apt upgrade
# reboot machine

• Install prerequisites

chiroptical

ability Semigroup m where
  assoc : m -> m -> m

-- Without unique, Monoid and Ask have the same hash
unique ability Monoid m where
  identity : m

use Semigroup assoc
use Monoid identity

chiroptical

ability State s where
  Get : s
  Put : s -> ()

runState : s -> Request (State s) a -> (s, a)
runState s = cases
  {State.Get -> k} ->
    handle k s with runState s
  {State.Put s -> k} ->
    handle !k with runState s

chiroptical

Stream.sum : '{Stream Nat} () -> Nat
Stream.sum = Stream.foldLeft (+) 0

> Stream.sum '(Stream.range 0 10)

ability Stream e where
  emit : e ->{Stream e} ()

Stream.range : Nat -> Nat ->{Stream Nat} ()
Stream.range n m =

chiroptical

sudo apt update
sudo apt upgrade
sudo apt install python3.7 python3.7-venv python3.7-distutils python3.7-dev gcc g++ libsndfile1
sudo snap install ffmpeg # Get ffmpeg 4
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.7 2
sudo update-alternatives --config python3 # Make sure 3.7 is selected
curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | python3
~/.poetry/bin/poetry config virtualenvs.in-project true
~/.poetry/bin/poetry install # If this fails because of pytorch, goto 11 else goto 12

chiroptical

chiroptical

{-# LANGUAGE LambdaCase #-}

module FindJust ( findJust ) where

import Control.Monad ( foldM )

findJust :: Monad m => [m (Maybe a)] -> m (Maybe a)
findJust = foldM (\acc x -> maybe x (pure . Just) acc) Nothing