Quint

Executable specs for reliable systems

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Executable

Quint

checked names and types

executable

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not executable

Abstract

Quint

define only what matters

Programming Languages

define how things happen, in detail

Modern

Quint

familiar syntax

CLI and your editor

Existing Spec Languages

math-y syntax

old GUI tools

bank.qnt


/// A state variable to store the balance of each account
var balances: str -> int
 
pure val ADDRESSES = Set("alice", "bob", "charlie")
 
action withdraw(account, amount) = {
  // Decrement balance of account by amount
  balances' = balances.setBy(account, curr => curr - amount)
}
 
// ...
 
/// Invariant: Account balances should never be negative
val no_negatives = ADDRESSES.forall(addr =>
  balances.get(addr) >= 0
)


$ quint run bank.qnt --invariant=no_negatives


An example execution:
 
[State 0] { balances: Map("alice" -> 0, "bob" -> 0, "charlie" -> 0) }
 
[State 1] { balances: Map("alice" -> -63, "bob" -> 0, "charlie" -> 0) }
 
[violation] Found an issue (44ms).
Use --seed=0x4e85b3a53f7ef to reproduce.
Use --verbosity=3 to show executions.
error: Invariant violated