Algebraic effects

[probeiuscorp]

Much of my love for pure functional programming comes from React, where context is everything for its usability and composability. As such, I very much want to add algebraic effects to the language. For example, consider division (syntax speculative):

effect DivideByZero *
div: forall a: Fraction e. a -> a -> (a + (effect DivideByZero e))

If we wanted to terminate the program upon a divide-by-zero:

main = doAllTheThings | handle {
  DivideByZero = undefined
}

If we wanted to wrap in Maybe:

mdiv = handle {
  DivideByZero = None
} . Some . div

Context lookup

effect config {
  timeout: Double
}
nestedCall: IO () & (effect config) = wait config.timeout

where the value config has type ({ timeout: Double }) & (effect config)

Semantics

findAverage = samples: List Num. {
  divAll: forall e. List $ (Num + DivideByZero e)
  divAll = samples <$> (div . length samples)
  sum: forall: e. Num + DivideByZero e
  sum = foldr (+) 0 divAll
} | .count