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In [1]

// Start with the interesting part.
uint256 a = 10
uint256 b = 3

a / b
a % b
a ** b

In [2]

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/ REPL RECIPES

Start from a working example.

96 practical cases for math, contracts, call data, debugging, forks, and VM helpers.

Browse with guides

Math & units

Math & unitsBasic arithmeticTry division, remainder, and powers with normal Solidity rules.Ready to run

Math & unitsSolidity 0.4.0 arithmeticRun original 0.4 syntax and keep typed results visible inline.Ready to run

Math & unitsEther and gas unitsConvert ether, gwei, and percentage calculations without a wrapper.Ready to run

Math & unitsSigned divisionSee how negative integer division and remainders round in Solidity.Ready to run

Math & unitsChecked overflowTrigger and inspect Solidity’s built-in overflow protection.Expected error

Math & unitsUnchecked wraparoundCompare unchecked arithmetic when a uint8 passes its maximum.Ready to run

Math & unitsBitwise and modular mathExplore shifts, masks, addmod, and mulmod.Ready to run

Math & unitsNumeric literal syntaxCompare digit separators, scientific notation, and hexadecimal literals.Ready to run

Math & unitsTime unitsTurn minutes, hours, days, and weeks into their integer second values.Ready to run

Math & unitsCompound assignmentUpdate one integer with arithmetic and shift assignment operators.Ready to run

Encoding & crypto

Encoding & cryptoKeccak hashHash text exactly as Solidity does onchain.Ready to run

Encoding & cryptoABI encode and decodeEncode mixed values and decode them back into typed variables.Ready to run

Encoding & cryptoPacked encodingCompare tightly packed bytes and their hash.Ready to run

Encoding & cryptoFunction selectorCalculate the first four bytes used to identify a function call.Ready to run

Encoding & cryptoDecode call dataRead the supplied transaction bytes as typed Solidity values.Uses context

Encoding & cryptoRecover a signerTest ecrecover inputs and see the zero address for an invalid signature.Ready to run

Encoding & cryptoString, Unicode, and hex literalsBuild UTF-8 strings and raw bytes with Solidity literal syntax.Ready to run

Encoding & cryptoType-safe ABI call encodingEncode function calldata with compile-time argument type checking.Ready to run

Encoding & cryptoABI signature encodingCompare encodeWithSignature with explicit selector encoding.Ready to run

Encoding & cryptoSHA-256 and RIPEMD-160Compare Solidity’s SHA-256 and RIPEMD-160 cryptographic helpers.Ready to run

Syntax & control flow

Syntax & control flowIf and else branchesFollow a value through ordered conditional branches.Ready to run

Syntax & control flowFor, break, and continueFilter loop iterations with continue and stop the loop with break.Ready to run

Syntax & control flowWhile and do-while loopsCompare a precondition loop with a loop that always runs once.Ready to run

Syntax & control flowTernary and boolean logicCombine a conditional expression with AND, OR, and negation.Ready to run

Syntax & control flowNamed function argumentsCall a function with named arguments in a different order.Ready to run

Syntax & control flowTuple destructuringReturn several values and skip an unwanted tuple position.Ready to run

Syntax & control flowNamed return valuesAssign named return variables without writing an explicit return tuple.Ready to run

Syntax & control flowTuple assignment swapSwap two existing variables in one destructuring assignment.Ready to run

Syntax & control flowRecursive internal callCall the current function internally until it reaches a base case.Ready to run

Types & storage

Types & storageDynamic arraysCreate, change, and inspect an in-memory array.Ready to run

Types & storageFixed arraysTry a fixed-size array literal and read its items.Ready to run

Types & storageStruct valuesCreate a struct and inspect each field immediately.Ready to run

Types & storageEnumsMove between a named enum state and its numeric value.Ready to run

Types & storageMapping storageWrite a mapping and inspect the resulting storage change.Ready to run

Types & storageUser-defined value typeWrap and unwrap a custom numeric Solidity type.Ready to run

Types & storageStorage array push and popAppend, update, and remove values from a dynamic storage array.Ready to run

Types & storageMemory reference aliasingSee two memory variables refer to the same array allocation.Ready to run

Types & storageLocal storage referenceModify a state array through a local storage reference.Ready to run

Types & storageDelete and default valuesReset value types to their Solidity defaults with delete.Ready to run

Types & storageInternal function valuesPass a Solidity function as a typed value to another function.Ready to run

Types & storageNamed nested mappingUse named mapping keys and values in a nested allowance table.Ready to run

Types & storageType informationInspect integer limits, contract bytecode, and an interface identifier.Ready to run

Types & storageBytes storage membersPush, index, and pop individual bytes in dynamic storage.Ready to run

Types & storageCalldata array sliceRemove a four-byte selector and decode the remaining calldata.Ready to run

Types & storageExplicit type conversionsConvert between integer widths, fixed bytes, and payable addresses.Ready to run

Types & storageExternal function membersInspect the address and selector carried by an external function value.Ready to run

Contracts & calls

Contracts & callsHelper functionDeclare a function beside loose statements and call it directly.Ready to run

Contracts & callsDeploy and call a contractCreate a contract in memory and call it in the same REPL session.Ready to run

Contracts & callsInheritance and overrideCheck virtual functions, super calls, and overrides.Ready to run

Contracts & callsImport a local libraryLoad a ready-made second file and use its library function.Includes files

Contracts & callsUse an imported repository fileImport a library from a repository-shaped path and call it from the REPL.Includes files

Contracts & callsInterface callCast a deployed contract to an interface and call it.Ready to run

Contracts & callsEmit and decode an eventSee indexed and normal event arguments beside their raw topics.Ready to run

Contracts & callsTry and catch a revertCall a contract that reverts and handle the result without ending the run.Ready to run

Contracts & callsConstant and immutable stateCompare a compile-time constant with a constructor-assigned immutable.Ready to run

Contracts & callsFunction modifierRun a function body through a reusable access-control modifier.Ready to run

Contracts & callsFunction overloadingResolve functions with the same name from their parameter types.Ready to run

Contracts & callsAbstract contract implementationImplement an abstract virtual function in a concrete contract.Ready to run

Contracts & callsLibrary using-for directiveAttach a library function to uint256 as a member function.Ready to run

Contracts & callsReceive and fallback functionsCompare an empty call with unmatched calldata on the same contract.Ready to run

Contracts & callsSalted contract creationDeploy a contract with CREATE2 syntax and a deterministic salt.Ready to run

Contracts & callsLow-level static callEncode calldata, use staticcall, and decode the returned bytes.Ready to run

Contracts & callsUser-defined operatorAttach the plus operator to a user-defined value type.Includes files

Contracts & callsTransient storageSet and clear transaction-scoped state with a transient variable.Ready to run

Contracts & callsSelective import aliasesRename imported symbols and use a file-level constant from another source.Includes files

Contracts & callsBase constructor argumentsPass constructor arguments from a derived contract to its base.Ready to run

Contracts & callsDelegatecall storage contextRun another contract’s code while writing to the caller’s storage.Ready to run

Contracts & callsExternal call optionsAttach value and gas options to a typed external function call.Uses context

Contracts & callsAnonymous eventEmit an anonymous event and inspect its indexed and data fields.Ready to run

Contracts & callsCustom storage layout baseMove a contract’s first storage slot to a chosen base position.Ready to run

Context & forks

Context & forksTransaction and block contextInspect caller, value, call data, block time, number, and chain ID.Uses context

Context & forksGlobal EVM informationRead block fees, randomness, coinbase, transaction gas price, and gas left.Uses context

Context & forksMessage function selectorCompare msg.sig inside a call with the function’s selector member.Ready to run

Context & forksSend payable valueFund the active call and forward ether to another contract.Uses context

Context & forksTimestamp deadlineTest time-based logic with a prefilled block timestamp.Uses context

Context & forksChain ID conditionTry logic that changes based on the selected chain ID.Uses context

Context & forksInspect a live addressSelect Fork and run; enter your RPC when prompted to inspect code and balance at a fixed block.Uses context

Context & forksCall USDC on a forkCall a deployed token at one Ethereum block and inspect its metadata, supply, and pool balance.Fork · RPC on Run

Debugging & errors

Debugging & errorsRequire messageTrigger a failed condition and jump back to its source line.Expected error

Debugging & errorsCustom errorRevert with typed data and inspect the failed run.Expected error

Debugging & errorsDivision by zeroSee a Solidity panic translated into a readable result.Expected error

Debugging & errorsAssert panicTrigger the panic reserved for a failed internal invariant.Expected error

Debugging & errorsYul switchUse inline assembly control flow and return the selected value.Debug view

Debugging & errorsTyped catch clausesHandle Error(string) and Panic(uint256) from external calls separately.Ready to run

Debugging & errorsArray bounds panicRead beyond a memory array and inspect Solidity panic code 0x32.Expected error

Debugging & errorsMemory-safe assemblyAnnotate an inline assembly block and perform arithmetic in Yul.Debug view

Debugging & errorsAssembly memoryRun Yul memory instructions and inspect stack, memory, and opcodes.Debug view

Debugging & errorsNested call traceCreate an external call and inspect its gas, input, output, and depth.Ready to run

VM helpers

VM helpersSet an address balanceUse vm.deal to fund any address for a local experiment.Ready to run

VM helpersWrite a storage slotPut a raw 32-byte value into a chosen contract slot.Ready to run

VM helpersRead a storage slotRead the raw value behind a normal Solidity state variable.Ready to run

VM helpersMove block timeChange block.timestamp during the run with vm.warp.Ready to run

VM helpersMove block numberChange block.number during the run with vm.roll.Ready to run

VM helpersInstall bytecodePlace tiny runtime bytecode at an address and call it.Ready to run

VM helpersLabel an addressGive an address a readable label while testing named actors.Ready to run

VM helpersKeep state between runsRun repeatedly to watch a stored counter continue from its last value.Keeps state