Pool metadata in one call

This is the flagship evs script: given a Uniswap V3 pool address, fetch the pool’s configuration (token0, token1, fee, current tick) and each token’s symbol and decimals — eight dependent reads, one eth_call, one fully typed result object.

The script

import { arg, evscript, t } from '@maxencerb/evs';
import { erc20Abi } from 'viem';

const uniswapV3PoolAbi = [
  {
    type: 'function',
    name: 'token0',
    stateMutability: 'view',
    inputs: [],
    outputs: [{ name: '', type: 'address' }],
  },
  {
    type: 'function',
    name: 'token1',
    stateMutability: 'view',
    inputs: [],
    outputs: [{ name: '', type: 'address' }],
  },
  {
    type: 'function',
    name: 'fee',
    stateMutability: 'view',
    inputs: [],
    outputs: [{ name: '', type: 'uint24' }],
  },
  {
    type: 'function',
    name: 'slot0',
    stateMutability: 'view',
    inputs: [],
    outputs: [
      { name: 'sqrtPriceX96', type: 'uint160' },
      { name: 'tick', type: 'int24' },
      { name: 'observationIndex', type: 'uint16' },
      { name: 'observationCardinality', type: 'uint16' },
      { name: 'observationCardinalityNext', type: 'uint16' },
      { name: 'feeProtocol', type: 'uint8' },
      { name: 'unlocked', type: 'bool' },
    ],
  },
] as const;

export const poolMeta = evscript(
  { name: 'poolMeta', args: [arg('pool', t.address)] },
  (s) => {
    const token0 = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'token0' });
    //    ^? Expr<'address'> — a runtime value, usable as the address of the NEXT call
    const token1 = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'token1' });
    const fee = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'fee' });
    const slot0 = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'slot0' });
    //    ^? readonly tuple of Exprs — one per slot0 output

    const symbol0 = s.call({ address: token0, abi: erc20Abi, functionName: 'symbol' });
    const symbol1 = s.call({ address: token1, abi: erc20Abi, functionName: 'symbol' });
    const decimals0 = s.call({ address: token0, abi: erc20Abi, functionName: 'decimals' });
    const decimals1 = s.call({ address: token1, abi: erc20Abi, functionName: 'decimals' });

    return s.return({
      token0,
      token1,
      fee,
      tick: slot0[1],
      symbol0,
      symbol1,
      decimals0,
      decimals1,
    });
  },
);

s.call types like viem’s readContract: the inline as const pool ABI and viem’s erc20Abi drive autocomplete for functionName and the output types. token0 comes back as Expr<'address'> — a handle to a value that exists only at run time — and goes straight into the address field of the symbol and decimals calls. Multi-output functions like slot0 return a readonly tuple of Exprs, so slot0[1] is the tick. See calls for the full s.call surface and values and types for how Expr handles work.

The dependency chain multicall cannot express

Trace the data flow: symbol0 is a call to token0, and token0 is the output of a call to the pool. Multicall3 encodes its whole batch client-side — every target address and every calldata blob must be known before the request is sent — so it can only batch independent reads. Here the targets of calls five through eight are unknown until calls one and two return, which forces a multicall user into two sequential round trips: one batch for the pool reads, then a second batch for the token reads built from the first batch’s results. evs records the dependency as a script and executes the whole chain inside a single eth_call, so the result arrives in one round trip regardless of how deep the chain goes. See why evs for the general argument.

Execution

Compile the script and spread toViem() into a plain viem readContract. The default mode is deployless: viem sends a two-parameter eth_call with the script’s init bytecode as code, so it works on every standard RPC provider and nothing is ever deployed.

import { arg, evscript, t } from '@maxencerb/evs';
import { createPublicClient, erc20Abi, http } from 'viem';

// --- the script from the previous section, unchanged ---

const uniswapV3PoolAbi = [
  {
    type: 'function',
    name: 'token0',
    stateMutability: 'view',
    inputs: [],
    outputs: [{ name: '', type: 'address' }],
  },
  {
    type: 'function',
    name: 'token1',
    stateMutability: 'view',
    inputs: [],
    outputs: [{ name: '', type: 'address' }],
  },
  {
    type: 'function',
    name: 'fee',
    stateMutability: 'view',
    inputs: [],
    outputs: [{ name: '', type: 'uint24' }],
  },
  {
    type: 'function',
    name: 'slot0',
    stateMutability: 'view',
    inputs: [],
    outputs: [
      { name: 'sqrtPriceX96', type: 'uint160' },
      { name: 'tick', type: 'int24' },
      { name: 'observationIndex', type: 'uint16' },
      { name: 'observationCardinality', type: 'uint16' },
      { name: 'observationCardinalityNext', type: 'uint16' },
      { name: 'feeProtocol', type: 'uint8' },
      { name: 'unlocked', type: 'bool' },
    ],
  },
] as const;

const poolMeta = evscript({ name: 'poolMeta', args: [arg('pool', t.address)] }, (s) => {
  const token0 = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'token0' });
  const token1 = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'token1' });
  const fee = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'fee' });
  const slot0 = s.call({ address: s.args.pool, abi: uniswapV3PoolAbi, functionName: 'slot0' });
  const symbol0 = s.call({ address: token0, abi: erc20Abi, functionName: 'symbol' });
  const symbol1 = s.call({ address: token1, abi: erc20Abi, functionName: 'symbol' });
  const decimals0 = s.call({ address: token0, abi: erc20Abi, functionName: 'decimals' });
  const decimals1 = s.call({ address: token1, abi: erc20Abi, functionName: 'decimals' });
  return s.return({ token0, token1, fee, tick: slot0[1], symbol0, symbol1, decimals0, decimals1 });
});

// --- compile once, call like any contract ---

const client = createPublicClient({ transport: http('https://ethereum-rpc.publicnode.com') });

const compiled = poolMeta.compile();

export const out = await client.readContract({
  ...compiled.toViem(), // { abi, code } — deployless eth_call
  functionName: 'poolMeta',
  args: ['0x88e6A0c2dDD26FEEb64F039a2c41296FcB3f5640'], // USDC/WETH 0.05% pool (mainnet)
});
// out.symbol0 → 'USDC' (string), out.decimals1 → 18 (number), out.token0 → 0x… (address)

No as const, no codegen step: the script value is its own literal-typed ABI, so args is typed readonly [pool: `0x${string}`] and out is fully inferred. For the state-override mode, block pinning, and the s.env caveats, see execution.

The result

The script’s return keys become the named components of a single tuple output, which viem decodes as an object:

{
  token0: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48',
  token1: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
  fee: 500,
  tick: 197180,
  symbol0: 'USDC',
  symbol1: 'WETH',
  decimals0: 6,
  decimals1: 18
}

(Values illustrative — tick moves with the market.) The TypeScript type matches: addresses as 0x${string}, fee/tick/decimals* as number (they fit in 48 bits), symbols as string.

Tip

Some legacy tokens are not clean ERC-20s (for example, a symbol() that returns bytes32 instead of string). A strict s.call reverts with EvsDecodeError when returndata does not decode; swap in s.tryCall and a default to tolerate them — see tryCall with a default and calls.

Run it from the repo

A runnable version of this example — examples/pool-meta — spawns a throwaway local anvil, deploys mock pool and token contracts, executes the compiled script deploylessly, and prints the typed result plus the script’s runtime bytecode size. For batching the same read over many inputs, continue with token balances.