Unison effect handling/testing sketch

effect.u

-- basic algebraic effect with just 2 capabilities
ability Effect where
    print : Text ->{Effect} ()
    input : {Effect} Text

-- `run main` will run the code
main = 'handle !prog with IOHandler

-- this is the program
prog _ =
    print "What's your name?"
    name = input
    print ("Hello " Text.++ name)
    ()

-- Here's how we want to test it!
--   expectPrint checks the call
--   sampleInput injects a sample input back into the program
--   result verifies the final output.

test> prog.tests.t1 =
  testEffect '(prog |> expectPrint "What's your name?"
                    |> sampleInput "Hakim"
                    |> expectPrint "Hello Hakim"
                    |> result ()
                    )         

IOHandler =
    cases
        {print e -> resume} ->
            printLine e
            handle !resume with IOHandler
        {input -> resume} ->
            x = !readLine
            handle resume x with IOHandler
        {u} -> u

expectPrint p r = handle !r with testPrintHandler p
sampleInput i r = handle !r with testInputHandler i
result res r = handle !r with testResultHandler res

testPrintHandler p =
    cases
        {print v -> next} ->
            if v == p then
                next
            else
                raise ("Expected " ++ p ++ " but got " Text.++ v)
        {w} -> raise "Unexpected" 
        
testInputHandler i =
    cases
        {input -> resume} ->
            '(resume i)
        {u} -> raise "No input found"

testResultHandler r =
    cases
        {w} -> if w == r then
                 "OK"
               else
                 raise "Wrong result!"

testEffect p =
    res = toEither p
    match res with
        Right x -> [Ok "Successful test!"]
        Left y -> [Fail y]