A Haskell client to connect to PayPal's REST API (v1)
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README.md

PayPal Client (for Haskell)

This library allows you to connect with PayPal's REST API V1 through Haskell.

Build Status

Master: Build Status Develop: Build Status

Warning Regarding Stability

During releases under 1.0.0, please use exact version numbers as bug fixes may require breaking changes while this library is unstable.

What Can It Do?

Currently implemented API resources include:

  • Auth
    • OAuth 2
  • Payments
    • Create a payment
    • Execute approved PayPal payment
    • Show payment details
    • List payments

Documentation and Usage Examples

Documentation can be found at the page for paypal-rest-client in Hackage.

The PayPal Monad and Session

PayPal's API uses OAuth 2 and therefore provides access tokens which expire. When this happens, the access token must be renewed. This problem is solved by the PayPalOperations monad. This monad can chain PayPal actions together which will be executed consecutively by execPayPal. If the token expires before an action is executed, the token is first renewed.

Suppose you need to create a new payment, then get that payment ID back as well as a list of all payment IDs. You could write this:

import Network.Payments.PayPal
import Network.Payments.PayPal.Payments

myOperations :: PayPalOperations (PaymentID, [PaymentID])
myOperations = do
  cRes <- createPayment $ CreateRequest ...
  lRes <- listPayments Nothing
  return (createResPayId cRes, map createResPayId $ listResPayments lRes)

Then, given you have a Config module with the credentials, you can execute the monad and get your results like so

import Config
import Network.Payments.PayPal

main :: IO ()
main = do
  payPalResult <- execPayPal sandboxUrl Config.clientId Config.secret
                             myOperations
  case payPalResult of
    Left err -> show err
    Right (newId, allIds) -> do
      putStrLn ("The new ID is: " ++ show newId)
      putStrLn ("All IDs are: " ++ show allIds)

The monad does not need to take error handling into account. If an error occurs, the monad receives a short circuit and the rest of the code is not executed. The error is simply returned to be handled. In the example, this means if createPayment fails, listPayments will never run.