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# Vesting Example

By
Travis Horn

# Handling Time

Lecture 3, Part 3

Lecture Video

Under most circumstances you can always tell whether a transaction will fail before submitting it to the blockchain. Validation can and does happen off-chain in a user's wallet.

However, the time when a wallet validates a transaction off-chain will be different than the time when the transaction arrives at a node. The txInfoValidRange of a ScriptContext handles this.

When a node processes a transaction it does basic checks first before running a script. It is at this time that the current time is checked to be within the valid time range.

By default, transactions use the infinite time range. This can be change, such as in the auction example from lecture 1.

Cardano uses slots as a measurement of time. Each slot is 1 second. So it's easy to go back and forth between real time and slots. The definition of a slot could possibly change in the future, so transactions shouldn't have a valid range that is too far in the future. A change to the slot definition requires a hard fork, which comes with an announcement at least 36 hours in advance.

txInfoValidRange has type POSIXTimeRange which contains an Interval and a POSIXTime. Interval optionally contains a LowerBound and an UpperBound.

There are a number of convenient functions for working with Intervals. Some examples:

  • member checks whether a value is included in an interval
  • always is an interval that covers every slot
  • from constructs an interval that starts at a given value and goes on forever
  • to is the opposite of from
  • before checks if a value is earlier than a given interval
  • after is the opposite of before

You can play around with intervals by starting up a Nix shell in plutus-apps

cd plutus-apps
nix-shell

Then change into this week's directory

cd ~/plutus-pioneer-program/code/week03

Start a REPL

cabal repl

Import the Interval module

import Plutus.V1.Ledger.Interval

See what an Interval looks like between slot 10 and 20

tenToTwenty = interval (10 :: Integer) 20
tenToTwenty
Interval {ivFrom = LowerBound (Finite 10) True, ivTo = UpperBound (Finite 20) True}

This can be read as "an interval with lower bound 10 inclusive (10 is included) and upper bound 20 inclusive" or even more simply "from slot 10 to 20".

You can check whether a value is a member of this interval

member 9 tenToTwenty
False

member 10 tenToTwenty
True

member 15 tenToTwenty
True

member 20 tenToTwenty
True

member 21 tenToTwenty
False

Another couple more interval examples

fromThirty = from (30 :: Integer)
toThirty = to (30 :: Integer)

member 999 fromThirty
True

member 999 toThirty
False

member 10 fromThirty
False

member 10 toThirty
True

You can get the intersection of two intervals

tenToTwenty = interval (10 :: Integer) 20
twelveToThirty = interval (12 :: Integer) 30

intersection tenToTwenty twelveToThirty
Interval {ivFrom = LowerBound (Finite 12) True, ivTo = UpperBound (Finite 20) True}

You can see we get a new interval where the two inputs intersect (12 to 20).