📖Do be do be do

based on Plotkin and Power’s algebraic effects

• and Plotkin and Pretnar’s handlers for algebraic effects

operators generalize functions and effects

• pure function is an operator with no effects

what bidirectional effect type system means?

what is effect polymorphism?

works in strict language (but with possibly delayed computations)

• “The absence of explicit plumbing in Frank depends crucially on the fact that Frank, unlike Haskell, has a fixed evaluation order.”

handling effects is just a function

state : S -> <State S>X -> X
state _ x            = x                 -- this catch-all does not include effects---only values
state s <get -> k>   = state s (k s)
state _ <put s -> k> = state s (k unit)

handling multiple effects

pipe : <Send X>Unit -> <Receive X>Y -> [Abort]Y
pipe <send x -> s> <receive -> r> = pipe (s unit) (r x)
pipe <_>           y              = y
pipe unit          <_>            = abort!