Voltaire Effect Contract Interactions

Query view/pure functions via eth_call (no wallet needed):

const getBalance = Effect.gen(function* () {
  const usdc = yield* Contract(usdcAddress, erc20Abi)
  const balance = yield* usdc.read.balanceOf(userAddress)
  return balance  // bigint
})

// Provide only ProviderService
const ProviderLayer = Provider.pipe(
  Layer.provide(HttpTransport('https://eth.llamarpc.com'))
)
const balance = await Effect.runPromise(getBalance.pipe(Effect.provide(ProviderLayer)))

Write Operations

State-changing functions require SignerService:

import { Secp256k1Live } from 'voltaire-effect/crypto/Secp256k1'
import { KeccakLive } from 'voltaire-effect/crypto/Keccak256'

const transfer = Effect.gen(function* () {
  const usdc = yield* Contract(usdcAddress, erc20Abi)
  const txHash = yield* usdc.write.transfer(recipientAddress, 1000000n)
  return txHash
})

// Full layer stack with crypto + signer
const WriteLayer = Layer.mergeAll(
  ProviderLayer,
  Secp256k1Live,
  KeccakLive,
  SignerLayer
)

await Effect.runPromise(transfer.pipe(Effect.provide(WriteLayer)))

Simulate Before Sending

Validate a write operation without actually sending:

const program = Effect.gen(function* () {
  const usdc = yield* Contract(usdcAddress, erc20Abi)
  const { result, request } = yield* usdc.simulate.transfer(recipient, amount)
  // result: true (simulated return value)
  // request: prepared transaction request
  return result
})

Event Queries

Query historical contract events:

const program = Effect.gen(function* () {
  const usdc = yield* Contract(usdcAddress, erc20Abi)
  const transfers = yield* usdc.getEvents({
    eventName: 'Transfer',
    fromBlock: 18000000n,
    toBlock: 'latest'
  })
  return transfers
})

Multicall Batching

Batch multiple contract reads into a single network call via Multicall3:

import { multicall } from 'voltaire-effect'

const program = Effect.gen(function* () {
  const results = yield* multicall({
    contracts: [
      { address: usdc, abi: erc20Abi, functionName: 'balanceOf', args: [user] },
      { address: dai, abi: erc20Abi, functionName: 'balanceOf', args: [user] },
      { address: weth, abi: erc20Abi, functionName: 'balanceOf', args: [user] },
    ],
    allowFailure: true  // Returns Either[] for partial failures
  })
  return results
})

With allowFailure: true, results are Either<Result, Error>[] - some calls can fail without aborting the batch.

Type Safety

The ABI definition drives compile-time type checking:

const usdc = yield* Contract(address, erc20Abi)

// Correct - matches ABI
usdc.read.balanceOf('0x...')  // ✓ address argument

// Wrong - TypeScript compile error
usdc.read.balanceOf(42)       // ✗ number is not address
usdc.read.nonExistent()       // ✗ function not in ABI

Per-Request Configuration

import { withTimeout, withRetrySchedule } from 'voltaire-effect'

// Timeout on a contract read
const balance = yield* usdc.read.balanceOf(addr).pipe(
  withTimeout("5 seconds")
)

// Retry a write
const txHash = yield* usdc.write.transfer(to, amount).pipe(
  withRetrySchedule(Schedule.exponential("500 millis").pipe(
    Schedule.jittered,
    Schedule.compose(Schedule.recurs(3))
  ))
)

Error Handling

program.pipe(
  Effect.catchTag('ContractCallError', (e) =>
    // Read/simulate failure (revert, invalid args, etc.)
    Effect.fail(new AppError(`Contract read failed: ${e.message}`))
  ),
  Effect.catchTag('ContractWriteError', (e) =>
    // Write failure (insufficient gas, nonce conflict, etc.)
    Effect.fail(new AppError(`Contract write failed: ${e.message}`))
  )
)

Real-World Example: Uniswap V2 Swap

const uniV2Router = yield* Contract(routerAddress, uniswapV2RouterAbi)

// 1. Get price quote
const amounts = yield* uniV2Router.read.getAmountsOut(
  amountIn,
  [tokenA, tokenB]
)

// 2. Calculate minimum output with slippage
const minOut = amounts[1] * 995n / 1000n  // 0.5% slippage

// 3. Execute swap
const txHash = yield* uniV2Router.write.swapExactTokensForTokens(
  amountIn,
  minOut,
  [tokenA, tokenB],
  recipient,
  BigInt(Math.floor(Date.now() / 1000) + 1200)  // 20 min deadline
)

Related Services

Reference

• Contract docs: https://voltaire-effect.tevm.sh/services/contract
• Multicall docs: https://voltaire-effect.tevm.sh/services/multicall
• Examples: https://voltaire-effect.tevm.sh/examples/contract-interactions