This directory contain two examples of simple contrtacts.
The first one, simple-contract-bool.ncl, defines simple contracts on booleans
and illustrates their use as pre-conditions and post-conditions of a function.
The second one, simple-contract-div.ncl, defines simple contracts on numbers
and illustrates the application of several contracts to one value. It is
expected to fail, to demonstrate basic error-reporting for contracts.
For illustrative purpose, those contracts are written as plain custom contracts:
functions Lbl -> Dyn -> Dyn. However, they are just boolean predicates here.
In this case, you should rather write them more succintly as predicates Dyn -> Bool and use contract.fromPred to obtain the corresponding contracts.
$ nickel -f simple-contract-bool.ncl
$ nickel -f simple-contract-div.ncl
You can try to break the one of the contracts of simple-contract-bool.ncl to
see them fail. Conversely, you can provide a valid value in
simple-contract-div.ncl to see the execution succeed.