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workflow library
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| {-# LANGUAGE KindSignatures #-} | |
| module Workflow where | |
| import Data.Bool (bool) | |
| data Workflow a r | |
| = Decision a (Workflow a r) (Workflow a r) | |
| | Guard a (Workflow a r) | |
| | Activity a (Workflow a r) | |
| | Conclusion a r | |
| -- | Output from guard step. Either stop and return a result, | |
| -- or keep going with the next step. | |
| data Guard r = Stop r | KeepGoing | |
| runWorkflow | |
| :: (Monad m) | |
| => (a -> m Bool) -- execute decision | |
| -> (a -> m (Guard r)) -- execute guard | |
| -> (a -> m ()) -- execute activity | |
| -> (a -> r -> m ()) -- execute conclusion | |
| -> Workflow a r | |
| -> m r | |
| runWorkflow fd fg fa fc workflow = | |
| let | |
| go = runWorkflow fd fg fa fc | |
| in | |
| case workflow of | |
| Decision desc t f -> | |
| fd desc >>= go . bool f t | |
| Guard desc next -> | |
| fg desc >>= \g -> case g of | |
| KeepGoing -> go next | |
| Stop r -> pure r | |
| Activity desc next -> | |
| fa desc *> go next | |
| Conclusion desc r -> | |
| r <$ fc desc r |
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