The `sic` code generator

sic is a tool primarily for generating the boilerplate code that makes it possible to seamlessly interact with a CSL contract from another language. Currently only Kotlin is supported as a target language. Because Kotlin is a JVM-based language sic indirectly supports other such languages like Java.

In addition to generating ergonomic and typesafe interfaces to CSL contracts, sic also supports compiling CSL declarations into different structured formats to be used by other applications. This aspect of sic is not the main focus of this documentation, but the functionality is described briefly at the end of this page (Core AST, Ontology, Signature).

Overview

When you have written a CSL contract and want to integrate it in a larger application you need some way of communicating with the system responsible for running the CSL contract. This can be done using the public API and one of the API clients, however, this means that you would have to take care of sending the right JSON-encoded data yourself, with no possibility of help from your language’s type checker.

sic generates mappings from the CSL data types to native data types in the target language, meaning that you can get help from the target language’s type checker and IDE support when building values of these types. Moreover, reports, events, and entrypoints in the contract are mapped to suitable constructs in the target language. Hence, instead of communicating directly using the Deon API, you can instead use specialized functions that use the generated native data types as input and output types, and which takes care of (de)serializing to the JSON format expected by Deon’s API. This makes it easier to work with the contract as you get the support that you would otherwise get when working in the target language. On top of that, it makes it dramatically less time-consuming to make changes to the CSL contract, as you will get the updated mappings for free by re-running sic, and any inconsistencies in the way you use the generated functions will be immediately caught by the target language’s typechecker.

Given a CSL contract, sic will generate the following components in the target language:

Data type definitions: Each data type in the contract will be mapped to a data type in the target language.
Report functions: For each report in the contract a corresponding function for invoking that report is created.
Event application functions: For each Event type in the contract a function for applying that event to a contract is created.
Contract instantiation functions: For each entrypoint in the CSL source a function for instantiating a contract from it is created.

Usage

sic is a command-line tool that works on Windows, MacOS, and Linux:

$ sic --help
sic <VERSION>

Usage: sic [-V|--version] [-n|--namespace NAMESPACE] [-t|--target ARG]
           [--stdlib PATH] [-w|--write] [-d|--destination PATH] [-m|--msgpack]
           FILES

Available options:
  -V,--version             Print version information
  -h,--help                Show this help text
  -n,--namespace NAMESPACE Namespace to put generated code in
  -t,--target ARG          Output target (default: Kotlin)
  --stdlib PATH            Use alternative CSL standard library
  -w,--write               Write generated source files to disk instead of just
                           printing them to stdout
  -d,--destination PATH    Root directory for generated source
                           files (default: "generated")
  -m,--msgpack             Use MessagePack serialization for serialized output
                           data.
  FILES                    Either: a list of .csl files to read, or: the string
                           "-" (a single dash), making sic read from stdin.

We shall use the contract “sic1.csl” for demonstration of how to use sic and for illustrating key points about the structure of the generated code:

type CustomerType
    | Regular Int
    | OneTime

type Address {
    street: String,
    number: Int,
    floor: Int
}

type Customer {
    name: String,
    age: Int,
    address: Address,
    customerType: CustomerType
}

type AddCustomer : Event {
    id : Int,
    customer : Customer
}

//  sum : List Int -> Int
val report sum = \ints -> foldl (\(x : Int) -> \y -> x + y) 0 ints

//  sumCustomerAge : List Customer -> Int
val report sumCustomerAge =
  \(customers : List Customer) ->
    sum (List::map (\(c : Customer) -> c.age) customers)

contract rec entrypoint shop = \total -> <*> a: AddCustomer
  where a.id = total then shop (total + 1)

Using Kotlin as the target language

The default target language of sic is Kotlin, and the default behaviour is to write the generated code to standard output. Thus, when we run the command

$ sic sic1.csl

it will print a bunch of Kotlin code to the terminal. If we pass the flag --write to sic it will write the code to disk:

$ sic --write contract.csl
Generating interface for sic1.csl
Wrote file generated/com/deondigital/api/contract/sic1/ContractDetails.kt
Wrote file generated/com/deondigital/api/contract/sic1/builtins.kt
Wrote file generated/com/deondigital/api/contract/sic1/sic1.kt
Wrote file generated/com/deondigital/api/contract/sic1/sic1.csl.kt
Wrote file generated/com/deondigital/api/contract/sic1/fromValue.kt
Wrote file generated/com/deondigital/api/contract/sic1/InstanceDispatcher.kt
Wrote file generated/com/deondigital/api/contract/sic1/ReportService.kt
Wrote file generated/com/deondigital/api/contract/sic1/ContractService.kt

We see here that one CSL contract is represented as Kotlin source files in the package com.deondigital.api.contract.sic1. The generated code will be put into the root directory generated/. Both the package name and the root directory can be changed with the flags --namespace (short: -n) and --destination (short: -d), respectively.

The file sic1.kt contains the interface and data definitions that enable us to interact with the CSL contract from Kotlin in a convenient manner. The file sic1.csl.kt is an embedding of the contract source in Kotlin. The remaining files contain code relevant for reporting (ReportService.kt), event application (ContractService.kt), and various internal marshalling/unmarshalling infrastructure. Moreover, the file ContractDetails.kt contains the class Sic1Module which implements the interface ContractDetails from the package com.deondigital:sic-preamble-core. This class is used to tie together all the generated contract-specific Kotlin code with the sic-compatible packages that implements the operations on specific backends (com.deondigital:sic-rest-operations, com.deondigital:sic-dbledger-operations). Thus, the generated code does not “know” about any ledger backend in and of itself – that is something that the application developer decides later by picking an implementation of the ContractOperations interface from com.deondigital:sic-preamble-core.

Data types

The file sic1.kt will contain, amongst many other things, the definitions of the following data types:

sealed class CustomerType : ToApiValue, ToPrettyString {
  companion object: FromApiValue<CustomerType> { /* ... */ }
  /* ... */
  data class Regular(val field0: Long) : CustomerType() {
    /* .. */
  }
  object OneTime : CustomerType() {
    /* .. */
  }
}
open class Address(
             val street: String,
             val number: Long,
             val floor: Long) : Record() {
  /* ... */
}
open class Customer(
             val name: String,
             val age: Long,
             val address: Address,
             val customerType: CustomerType) : Record() {
  /* ... */
}

We have left out a lot of details here, but the snippet demonstrates how a sum type in CSL is converted to a sealed class in CSL with a subclass for each constructor while a CSL record type is converted to an open class. The names of parameters of an open class match the names in the CSL record. Base types such as Int and String are represented by their native counterparts in Kotlin: kotlin.Long and kotlin.String.

Reports

The CSL reports are converted to functions in the target language with appropriate types. That is, the input and output types are mappings from the CSL type to the target language type as described in the above section.

In our generated Kotlin code, we find the following class:

open class ReportService(/* ... */) {

  fun sum(ints: List<Long>) : CompletableFuture<Long> = /* implementation */
  fun sumCustomerAge(customers: List<Customer>) : CompletableFuture<Long> = /* implementation */
}

The class com.deondigital.api.contract.sic1.ReportService declares two functions, one for each of the CSL reports in sic1.csl. Input and output types of the functions are mapped from the corresponding CSL types; note that the CSL List a type is mapped to Kotlin/Java’s List<T> type.

To get an instantiated report service, one must construct an instance of the ContractOperations class and project out the reports field of it. The following snippet illustrates how one could run a report up against the Deon REST API using this interface:

val apiClient = DeonAPIClient(API_URL) // Connect to the ledger
// Construct a 'RESTContractOperations' (from 'com.deondigital:sic-rest-operations')
// specialised to the code we've just generated. This uses the 'Sic1Module' class that
// implements the 'ContractDetails' interface.
val ops = RESTContractOperations(apiClient, Sic1Module())
val reportService = ops.reports
val s = reportService.sumCustomerAge(listOf(
    Customer("bob", 42, Address("Main st.", 1, 5), CustomerType.OneTime),
    Customer("alice", 30, Address("Main st.", 10, 2), CustomerType.Regular(1)))
).get() // == 72

Contract instantiation

Every entrypoint declaration in a CSL contract represents a possible instantiation point of a contract in the system. The generated Kotlin code for sic1.csl contains the following class:

class shop<EventApplyResult>(/* ..., */
             val total: kotlin.Long
) : ContractInstance<ContractService<EventApplyResult>, Event>(/* ... */) {
  companion object {
    fun <EventApplyResult> instantiate(/*...,*/ total: Int) =
      /* ... */
    fun <EventApplyResult> getInstance(ops: ContractOperations, contractId: ContractId) =
      /* ... */
  }
}

The shop contract entrypoint is the basis of a class with the same name that holds a static method instantiate. When used, the instantiate method gives an instance of shop that can be used to query the state of the running contract and to apply events. It also provides access to instantiation arguments for the contract. The class shop implements the interface ContractInstance from com.deondigital:sic-preamble-core, using some of the generated classes as concrete type paramters. This is used to tie the code generated here together with the machinery provided by the ledger-specific preamble packages in a (Kotlin) type-preserving way.

In order to make it possible to use any backend, the instantiate function takes a ContractOperations object that describes how contract state is being managed. Moreover, all instantiation functions take the same parameters as the CSL entrypoints (mapped to the Kotlin type), plus two additional optional parameters:

MetaArgs that can be used to supply additional information about the contract that will be instantiated, such as which peers should be used in the Corda backend and which name will be given to the contract instance
timeProvider to manage how event timestamps are set.

To instantiate the shop entrypoint using the REST backend, we use the RESTContractOperations implementation of ContractOperations:

val apiClient = DeonAPIClient(API_URL)
// Construct a ContractOperations for a REST backend and use the types in 'Sic1'
val ops = RESTContractOperations(apiClient, Sic1())
// Instantiate the contract 'shop'
val contract1 = shop.instantiate(ops, 42)
// Instantiate a new contract from 'shop'
val contract2 = shop.instantiate(ops, 11)
// Instantiate yet another contract from 'shop',
// but give the instance a custom name
val namedContract = shop.instantiate(ops, 47, MetaArgs(name = "shopContract47"))

Event application

Every subtype of Event in the contract gets mapped to a function that applies an event of that type to a running contract. Any fields that the event record might have is represented as a parameter to the event application function.

The classes created with .instantiate(...) exposes a field applyEvent that allows application of events as functions, i.e. AddCustomer(). Because the AddCustomer event record contains two fields in addition to the fields in Event, id : Int and customer : Customer, the Kotlin function accepts two parameters corresponding to the fields. The return type is parameterized like it was the case for contract instantiation from Kotlin.

The example snippet below uses the contract contract1 instantiated above:

// Now we can apply two 'AddCustomer' events on the contract:
contract1.applyEvent.AddCustomer(0, Customer("bob",
                                 42,
                                 Address("Main st.", 1, 5),
                                 CustomerType.OneTime));
contract1.applyEvent.AddCustomer(1, Customer("alice",
                                 30,
                                 Address("Main st.", 10, 2),
                                 CustomerType.Regular(1)));

Gradle plugin

The sic boilerplate generator comes with a Gradle plugin that makes it simple to integrate it into projects. To use it, the root gradle project will need the following additions:

build.gradle must include:

plugins {
  id 'com.deondigital.gradle-sic-plugin' version "<CSL_VERSION>" // replace CSL_VERSION with the current version
}

csl {
  destinationDir       = 'generated/sic/'
  cslDir               = 'src/main/csl/'
  sicNamespace         = project.group
}

The plugin provides the following tasks (use gradle tasks for an overview):

Task	Description
generateKotlinFromCSL	Generates Kotlin code with `sic`
compileCSL	Compiles your CSL code into a `.cslpkg` bundle which is used by the runtime

There are a number of additional internal tasks exposed by the plugin, but they should generally not be used in most applications.

If you need IDE support for working with generated classes, add the following to the relevant project. This will make it possible for, e.g., IntelliJ IDEA to show the generated code.

sourceSets {
  main.kotlin {
    srcDir 'generated/sic/kotlin' // matches csl.destinationDir + '/kotlin'
  }
}

Note that you will need to add dependencies on com.deondigital:sic-preamble-core.

The `@deondigital/sic` NPM package

The sic tool is distributed in the NPM package @deondigital/sic. It provides a handy way to install sic:

$ npx @deondigital/sic

This will download the latest version of sic and run it.

Compile CSL code to a `.cslpkg` file

sic can compile a CSL file (or a deon-project) to a .cslpkg file which is used by the CSL runtime.

$ sic compile sic1.csl --output sic1.declaration.cslpkg
Generating interface for sic1.csl
No project file found
Wrote file generated/./sic1.declaration.cslpkg

Manually referencing the .cslpkg is only necessary in advanced use cases.

The `.cslpkg` file

The .cslpkg contains four distinct components that you can extract using the provided methods in the runtime library.

A representation of core AST

The .cslpkg file contains a structured core representation of a CSL project. This core representation is used by the evaluator.

Note that this core representation is the result of several steps of internal processing that among other things strips away type information.

A representation of type definitions

The Ontology of a contract is a representation of all types used in a contract. The Ontology component in the .cslpkg file includes the preamble and built-ins. The output is an array of ontology elements. Each element has the following form:

A representation of declaration signature

It is possible to get a representation of the types of all top-level definitions in a CSL file. This is called the Signature of the CSL declaration. The .cslpkg file contains the Signature of the input CSL declaration, including the signature for the the preamble and built-ins.

Projects with multiple CSL files

CSL contracts can be grouped into projects by defining a file called deon-project in a folder. This file contains a newline-separated list of relative or absolute paths to CSL files. Its presence in the folder foo means that the folder is a “project”, and that the CSL files should be loaded in the order specified in the deon-project file. For example, the following deon-project file specifies a project that contains the files sic1.csl, sic2.csl, and sic3.csl:

sic1.csl # comments are also supported
subfolder/sic2.csl
/absolute/folder/sic3.csl

Contracts that are part of a deon-project are typechecked in the context of all contracts that come before them in the project specification. Thus, sic1.csl may only refer to names declared in the same file or in the standard library, whereas anything declared in sic1.csl is in scope in sic2.csl, and anything in sic1.csl and sic2.csl is in scope in sic3.csl.

Using projects in `sic`

Given the project file myproject/deon-project:

sic1.csl
sic2.csl

Running the command:

$ sic generate --write --target Kotlin --namespace org.foo myproject

Will output the following:

Wrote file generated/org/foo/myproject/builtins.kt
Wrote file generated/org/foo/myproject/sic1.kt
Wrote file generated/org/foo/myproject/sic1.csl.kt
Wrote file generated/org/foo/myproject/sic2.kt
Wrote file generated/org/foo/myproject/sic2.csl.kt
Wrote file generated/org/foo/myproject/fromValue.kt
Wrote file generated/org/foo/myproject/InstanceDispatcher.kt
Wrote file generated/org/foo/myproject/ReportService.kt
Wrote file generated/org/foo/myproject/ContractService.kt
Wrote file generated/org/foo/myproject/ContractDetails.kt

The sic code generator