cedar

This is alpha-level stuff.

Cedar is a small web service declaration language. You declare your service using this language and then use that declaration to generate client and server code for a number of programming languages.

Goals

• A single transport (http) and serialization format (json).
• Simple, consolidated tooling. All functionality must live under this repository and must be distributed under one package.
• Aim to be an 85% solution. Be the most simple thing that covers the widest array of use cases. Never add complexity for the sake of covering fringe use cases.
• Generated source code must be idiomatic to the generated language.
• Generated source code must be human-readable.

Installation

pip3 install cedar

Languages

Cedar currently targets Elm (clients) and Go (servers) source code.

Go

cedar generate go --help

Requirements

Generated Go code has no external dependencies, but it does require at least Go version 1.6.

Elm

cedar generate elm --help

Requirements

Generated Elm code currently requires Elm 0.17 and the following packages:

• elm-community/json-extra 1.x
• lukewestby/elm-http-builder 2.x

The Cedar language

A Cedar specification consists of one or more toplevel declarations. All toplevel declarations must be valid enums, unions, records or fns.

Example

enum Role { User, Mod, Admin }

record User {
  id Int
  email String
  role Role
}

fn getUsers() [User]
fn getUser(id Int) User?
fn deleteUser(id Int) Bool

Types

There are 5 builtin types: Bool, Int, Float, String and Timestamp.

List types are declared using the [t] syntax (eg. [String]), dict types are declared using the {String: t} syntax, and nullable types are declared using the t? syntax.

Enums

enum Status { Ready, Done, Failed }

Enums introduce new types (named after the enum) whose values are constrained to the tags defined in the enum. The tags inside an enum are serialized as strings. For example, a record attribute with the type Status can contain one of the following JSON values: "Ready", "Done" and "Failed".

Unions

union Resource { Post, Comment }

Unions join multiple types under a single new type.

Records

record Post {
  id Int
  title String
  content String
  publishedAt Timestamp
}

Functions

fn createPost(title String, content String, publishedAt Timestamp?) Post

Editor support

• cedar-mode for Emacs