Stamina

A retry Haskell library for humans:

• Exponential backoff with jitter between retries.
• Limit the attempts of retries and total time.
• Stamina.HTTP for retrying retriable Network.HTTP.Client exceptions.
• Introspectable retry state for logging using RetryStatus, including the exception that occured.
• Support resetting the retry state when the action is long-running and an attempt works.

API

• RetryAction
• RetryStatus
• defaults
• retry
• retryOnExceptions

Example

import qualified Stamina
import Control.Monad.Catch (throwM)

go :: IO ()
go = do 
    defaults <- Stamina.defaults
    Stamina.retry defaults $ \retryStatus -> do
        throwM $ userError "nope"

Example to catch specific exceptions

isDoesNotExistError :: IOError -> Stamina.RetryAction
isDoesNotExistError _ = Stamina.Retry

go2 :: IO ()
go2 = do 
    defaults <- Stamina.defaults
    Stamina.retryOnExceptions defaults (return . isDoesNotExistError) $ \retryStatus -> do
        throwM $ userError "nope"

Development

1. Install devenv.sh.

2. devenv shell

3. stack build

Credits

• Heavily inspired by stamina for Python.
• retry as case study for what needs to be supported.

Test setup

main = undefined