ReaderT Tutorial

Quickstart

Ensure that you have installed stack:

curl -sSL https://get.haskellstack.org/ | sh

In the project root run:

stack --install-ghc test

The above command will install the appropriate compiler and build the project libraries and test suite.

Using a ReaderT

Using functions from the module CoinberryApi and the App type provided by Transformer build a program that will fetch the prices for a given currency and display it.

An example of usage would be:

CURRENCY=BTC stack exec price
You can buy BTC for 6761.49

The currency should be passed in an environment variable and can be one of BTC, ETH, LTC or XRP.

The program should use all effectful computations from the Context, never importing directly functions that run in IO.

Creating tests

In the test suite we want to mock all effectful computations from IO. Namely the HTTP GET requests and the calls to print to the console. In order to achieve this model the necessary functions as part of the Context in the App type and supply the mock functions when running the tests.