purescript-web3

A Purescript Client for the Web3 API

purescript-web3 is a library for interacting with an ethereum node purescript. At the moment it covers most endpoints of the web3 api, which means it is suitable for sending transactions, querying blockchain state and metadata, and monitoring events.

Using purescript-web3-generator it is also possible (and recommended) to generate a library from a set of smart contract abis which is capable of templating transactions and event filters/watchers. The README has instructions for getting started.

We do not yet have a build tool similar to truffle, but if you are looking for a template of how to use truffle and write your tests using purescript, check out out the purescript-web3-tests

To see an example project using all of the purescript-web3 tools and with thermite/react ui, check out purescript-web3-example.

Build Instructions

> npm install
> npm run build
> npm run test

Documentation

Module documentation is published on Pursuit.

Examples

Suppose we have the following solidity smart contract:

contract TupleStorage {
    
    uint x;
    uint y;
    
    event TupleSet(uint newX, uint newY);
    
    function setTuple(uint _x, uint _y) public {
        x = _x;
        y = _y;
        TupleSet(_x, _y);
    }
    
}

If we used purescript-web3-generator, we are given a function with the following signature:

setTuple :: forall e.
            TransactionOptions NoPay 
         -> {_x :: UIntN (D2 :& D5 :& DOne D6), _y :: UIntN (D2 :& D5 :& DOne D6)} 
         -> Web3 HexString 

It's pretty clear what this function is doing, but let's look at the TransactionOptions. This record keeps track of, for example, who is the transaction from, what contract address is it going to, is there ether being sent, etc. In this case, the function is not "payable", so this is indicated in the type of the TransactionOptions. It is set using lenses like:

setTupleOpts :: TransactionOptions NoPay
setTupleOpts = defaultTransactionOptions
             # _from ?~ myAddress
             # _to ?~ tupleStorageAddress

Now for the TupleSet event. In order to start an event watcher, we need to establish the Filter, which specifies things like the range of blocks we are interested in, and how to find that particular contract and topic. Again, if you're using web3-generator, things are a lot simpler:

tupleFilter :: Filter TupleSet
tupleFilter = eventFilter (Proxy :: Proxy TupleSet) tupleStorageAddress 
           # _fromBlock .~ BN 100

We also need to pass a callback to the event watcher that performs some action and decides whether or not to unregister the filter. For example, we could set up an event monitor starting from block 100 and continuing until the two coordinates that are set are equal:

event tupleFilter $ \(TupleSet {newX,newY} -> do
  liftAff <<< log $ "Received New Tuple : " <> show (Tuple newX newY) 
  if newX == newY
    then pure TerminateEvent
    else do
      _ <- performAction newX newY
      pure ContinueEvent

For more examples, check out the foam kitty monitor, the example project using thermite, or the purescript-web3-tests repo.

Resources

• web3 RPC spec
• solidity documentation