nickel/examples

Examples

This directory contains an evolving selection of examples of Nickel programs.

Execution

Please follow the main repository's README instructions to have a working nickel executable. You can then either use the command line or launch an interactive session. Play with the values to see contracts failing when fed with invalid data!

From the command line

• Base values: some examples just return numbers, strings or booleans. You can run them directly:

  $ nickel eval fibonacci.ncl
  55
  

• Configurations: some examples return records representing configuration. You can run them directly as well, or use the export subcommand to see the result serialized as JSON, which might be more readable:

  $ nickel export merge-main.ncl
  {
    "firewall": {
    ...
  }
  

  Alternatively, you can query individual elements of a configuration, showing documentation and other metadata:

  $ nickel query --field kind record-contract.ncl
    • contract: [|'ReplicationController, 'ReplicaSet, 'Pod|]
    • documentation: The kind of the element being configured.
  

From the REPL

First start the REPL:

$ nickel repl
nickel>

• Just import a file directly to evaluate it:

  nickel> import "fibonacci.ncl"
  55
  
  nickel>
  

• Use std.serialize to have the same behavior as the export subcommand and print the result as JSON:

  nickel> builtin.serialize 'Json (import "merge-main.ncl")
  "{
      \"firewall\": {
      ...
  }"
  
  nickel>
  

• Use :query to retrieve information and documentation about a field:

  nickel> let config = import "record-contract.ncl"
  nickel> :query config.kind
  • contract: [| 'ReplicationController, 'ReplicaSet, 'Pod |]
  • documentation: The kind of the element being configured.
  
  nickel>