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The Bosque programming language is an experiment in regularized design for a machine assisted rapid ...

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Bosque Programming Language

Licensed under the MIT License PR's Welcome Build Status

The Bosque Project

The Bosque Programming Language project is a ground up language & tooling co-design effort focused on investigating the theoretical and the practical implications of:

  1. Explicitly designing a code intermediate representation language (bytecode) that enables deep automated code reasoning and the deployment of next-generation development tools, compilers, and runtime systems.
  2. Leveraging the power of the intermediate representation to provide a programming language that is both easily accessible to modern developers and that provides a rich set of useful language features for developing high reliability & high performance applications.
  3. Taking a cloud-development first perspective on programming to address emerging challenges as we move into a distributed cloud development model based around microservices, serverless, and RESTful architectures.

The Role of Intermediate Representations

Compiler intermediate representations (IRs) are traditionally thought of, and designed with, a specific source language (or languages) in mind. Their historical use has primarily been as an intermediate step in the process of lowering a source language program, with all of the associated syntactic sugar, into a final executable binary. However, over time they have become increasingly important in supporting program analysis and IDE tooling tasks. In these scenarios choices which were did not matter in the context of the compilation workflow can have major negative impacts.

In the Bosque project we ask the question of what happens if the IR is designed explicitly to support the rich needs of automated code reasoning, IDE tooling, etc. With this novel IR first perspective we are exploring a new way to think about and build a language intermediate representation and tools that utilize it. Our initial experiments show that this empowers a range of next-generation experiences including symbolic-testing, enhanced fuzzing, soft-realtime compilation with stable GC support, API auto-marshaling, and more!

Regularized Programming

Many features that make the Bosque IR amenable for automated reasoning involve simplifying and removing sources of irregularity in the semantics. These regularizations also simplify the task of understanding and writing code for the human developer. Inspired by this idea the Bosque project is building a new regularized programming language that takes advantage of the features of the IR.

The Bosque Programming Language builds on the strengths of classical Functional Programming, modern TypeScript/Node.js, and the power of the new IR. The result is a language that simultaneously supports the kind of high productivity development experience available to modern developers while also providing a resource efficient and predictable runtime, scaling from small IoT up to heavily loaded cloud services. In addition to bringing all the expressive power expected from a modern language, the Bosque language also introduces several novel features like Typed Strings and API Types, that directly address challenges faced by developers working in a distributed cloud based world.

Cloud First Development

The move into cloud based development, with architectures based around microservices, serverless functions, and RESTful APIs, brings new challenges for development. In this environment an program may interoperate with many other (remote) services which are maintained by different teams (and maybe implemented in different languages). This forces APIs to use least-common denominator types for interop and creates the need for extensive serialize/deserialize/validate logic. Further, issues like cold-service startups, 95% response times, resiliency and diagnostics, all become critical but have not been design considerations in most traditional languages.

The Bosque project takes a cloud and IoT first view of programming languages. Thus, it includes features like API Types to simplify the construction and deployment of REST style APIs. Application initialization design provides 0-cost loading for lighting fast (cold) startup. Choices like fully determinized language semantics, keys and ordering, and memory behavior result in a runtime with minimal performance variability and enable ultra-low overhead tracing.

Powering the Future of Programming

An overarching theme of the Bosque project is increasing the ability of automated tools to reason about and transform code. This mechanization is a foundational part of unlocking the future of using AI and Synthesis in the development pipeline. The ability to mechanically reason about the semantics of a program via symbolic means is a key enabler to synthesizing novel and useful code components using examples or conditions. Bosque’s fully determinized and loop free design can also help facilitate the development and application of automated program differentiation. These are open problems but, just as we saw how Bosque unlocks value in classical tooling/compilation scenarios, we are excited to see what it can do to power the AI and Synthesis programming revolution.

Note: This repository and code are currently still experimental. This means that the language is subject to revision, there are bugs and missing functionality, and the performance is limited.


August 2020: An on demand version of the Bosque Webinar with Q&A from May 27th is now available.


Small samples of code and unique Bosque tooling are below in the Code Snippets and Tooling sections. A rundown of notable and/or unique features in the Bosque language is provided in the language overview section 0. For a look at how the language works and flows in the large please see the code for a simple tic-tac-toe program.

Detailed Documentation, Tutorials, and Technical Information: * Language Docs * Library Docs * Tutorials - Coming Eventually! * Technical Papers * Contribution guidelines

Code Snippets

Add 2 numbers:

function add2(x: Int, y: Int): Int {
    return x + y;

add2(2, 3) //5 add2(x=2, y=3) //5 add2(y=2, 5) //7

All positive check using rest parameters and lambda:

function allPositive(...args: List): Bool {
    return args.allOf(fn(x) => x >= 0);

allPositive(1, 3, 4) //true

Tuples and Records:

function doit(tup: [Int, Bool], rec: {f: String, g: Int}): Int {
    return tup.0 + rec.g;

doit([1, false], {f="ok", g=3}) //4

Sign (with optional argument):

function sign(x?: Int): Int {
    var y: Int;

if(x == none || x == 0) {
    y = 0;
else {
    y = (x > 0) ? 1 : -1;

return y;


sign(5) //1 sign(-5) //-1 sign() //0

Nominal Types Data Invariants: ``` concept WithName { invariant $name != "";

field name: String;


concept Greeting { abstract method sayHello(): String;

virtual method sayGoodbye(): String {
    return "goodbye";


entity GenericGreeting provides Greeting { const instance: GenericGreeting = [email protected]{};

override method sayHello(): String {
    return "hello world";


entity NamedGreeting provides WithName, Greeting { override method sayHello(): String { return String::concat("hello", " ",; } }

[email protected]{}.sayHello() //"hello world" GenericGreeting::instance.sayHello() //"hello world"

[email protected]{}.sayHello() //type error no value provided for "name" field [email protected]{name=""}.sayHello() //invariant error [email protected]{name="bob"}.sayHello() //"hello bob" ```

Validated and Typed Strings: ``` typedef Letter = /\w/; typedef Digit = /\d/;

function fss(s1: SafeString): Bool { return s1.string() == "3"; }

Digit::accepts("a"); //false Digit::accepts("2"); //true

fss("1234") //type error String is not a SafeString fss(SafeString::from("a")) //type error incompatible SafeString types fss(Digit'a') //type error 'a' is incompatible with Digit fss(SafeString::from("a")) //runtime error 'a' is incompatible with Digit fss(SafeString::from("3")) //true ```

entity StatusCode provides Parsable {
    field code: Int;
    field name: String;

override static tryParse(name: String): Result<statuscode string> {
    return switch(name) {
        case "IO"      =&gt; ok([email protected]{1, name})
        case "Network" =&gt; ok([email protected]{2, name})
        case _         =&gt; err("Unknown code")


function isIOCode(s: StringOf): Bool { return s == StatusCode'IO'; }

isIOCode("IO"); //type error not a StringOf isIOCode(StatusCode'Input') //type error not a valid StatusCode string isIOCode(StringOf::from("Input")) //runtime error not a valid StatusCode string

isIOCode(StatusCode'Assert') //false isIOCode(StringOf::from("IO")) //true

let ec: StatusCode = [email protected]'IO'; assert(ec.code == 1); //true

Structural, Nominal, and Union Types (plus optional arguments) ``` entity Person { field name: String; }

function foo(arg?: {f: Int, n?: String} | String | Person): String { if(arg == none) { return "Blank"; } else { return switch(arg) { type Record => arg.n ?| "Blank" type String => arg type Person => }; } }

foo() //"Blank" foo(none) //Type error - none not allowed foo("Bob") //Bob foo([email protected]{name="Bob"}) //Bob foo({f=5}) //"Blank"

foo({f=1, n="Bob"}) //"Bob" foo({g=1, n="Bob"}) //Type error - Missing f property ```

Pre/Post Conditions ``` entity Animal { invariant $says != "";

field says: String;


function createAnimal(catchPhrase: String): Animal { return [email protected]{says=catchPhrase}; }

function createAnimalPre(catchPhrase: String): Animal requires catchPhrase != ""; { return [email protected]{says=catchPhrase}; }

function createAnimalPreSafe(catchPhrase: String): Animal requires release catchPhrase != ""; { return [email protected]{says=catchPhrase}; }

typedef ErrData = {msg: String, data?: Any};

entrypoint function getSays(animal: String, catchPhrase: String): Result validate animal != "" or return err({ msg="Invalid animal" }); validate catchPhrase != "" or return err({ msg="Invalid catchPhrase" }); { return ok(String::concat("The ", animal, " says ", createAnimal(catchPhrase).says)); }

createAnimal("woof woof") //ok always createAnimal("") //fails invariant in debug createAnimalPre("") //fails precondition in debug but not release createAnimalPreSafe("") //fails precondition in all build flavors

getSays("dog", "woof") //[email protected]{value="The dog says woof"} getSays("", "woof") //[email protected]{error={ msg="Invalid animal" }} getSays("dog", "") //[email protected]{error={ msg="Invalid catchPhrase" }} ```

API Types



Symbolic Testing

Bosque provides a powerful new way to test your applications. Unit-testing is a great way to ensure that code works as expected and to prevent accidental changes to behavior when adding new features or fixing bugs. However, writing and maintaining large numbers of tests can be a tedious and time consuming task. To help with this Bosque provides a symbolic testing harness that augments unit-testing and provides high coverage for bugs that result in runtime failures -- arising either as builtin language errors or from failed user provided pre/post/invariant/assert conditions.

The symtest tool implements the symbolic testing algorithm and works as follows. Given the application shown below: ``` namespace NSMain;

global ops: Set = [email protected]{ "negate", "add", "sub" };

function checkIntBounds(arg: Int?): Bool { //our calculator is for small numbers -- maybe use BigInt later return arg == none || ((-100 <= arg) && (arg <= 100)); }

entrypoint function processOp(op: String, arg1: Int, arg2: Int?): Int requires release NSMain::ops.has(op); requires release checkIntBounds(arg1) && checkIntBounds(arg2); //requires release (op == "add" || op == "sub") ==> arg2 != none; { if(op == "negate") { return -arg1; } else { assert(arg2 != none);

    if(op == "add") {
        return arg1 + arg2;
    else {
        return arg1 - arg2;

} ```

Assuming this code is in a file called

then we can run the following command to check for errors: ```

node bin\runtimes\symtest\symtest.js process_op.bsq ``` Which will report that an error is possible.

Re-running the symbolic tested with model generation on as follows: ```

node bin\runtimes\symtest\symtest.js -m division.bsq ``

Will report that an error is possible when
op == "negate"
arg2 == none
. Note that the tester was aware of the precondition
requires _ops.has(op)
and so did not generate any *spurious* failing test inputs (such as

Un-commenting the second requires line tells the tester that this, and similar errors are excluded by the API definition, and re-running the tester will now report that the code has been verified up to the bound.

Note: we recommend specifying preconditions as always checked,

requires release
, on entrypoint functions to ensure that these externally exposed API endpdoints are not misused.

More details on this symbolic checker can be found in the readme.

Ahead-of-Time Compilation

To provide the best performance Bosque supports the generation of standalone command-line executables via the

tool. This tool, and the design of the Bosque runtime, are designed to provide:
  1. Fast cold start response time by precompiling startup logic directly into constant values whenever possible and minimizing the number of operations required to start handling user input.
  2. Stable execution behavior over time and possible inputs.
    • The GC is a novel reference counting with eager free implementation to minimize memory footprint and prevent any indeterminate GC jitter.
    • The runtime itself uses sorted container implementations for Sets/Maps so that the variance between average and worst case costs of operations is minimized and to protect against pathological behaviors (like extreme hash-code collisions).
  3. Safe recursion is available with the [TODO] flag. This compiles recursive functions into a CPS form that uses constant stack space, eliminating any possible Out-of-Stack issues, and allows us to preserve the full call-stack in all debug builds.

A simple example use is to create a file called "max.bsq" with the following code: ``` namespace NSMain;

entrypoint function main(x: Int, y: Int): Int { return (x > y) ? x : y; }

Then run the following command to produce the `max.exe` (on Windows executable) which can then be invoked with:

node impl\bin\runtimes\exegen\exegen.js -o max.exe max.bsq ``

Which will create an executable named
max.exe` in the current directory.

Running this executable: ```

max.exe 1 5 ``

Will output

More details on the

tool can be found in the readme.

Using the Bosque Language

The current focus of the Bosque project is core language design. As a result there is no support for packaging, deployment, lifecycle management, etc.


In order to build the language the following are needed:

  • 64 bit Operating System
  • The LTS version of node.js ( According to your OS )
  • Typescript (install with:
    npm i typescript -g
  • A C++ compiler -- by default
    on Windows/Linux/Mac

Build & Test


directory contains the reference implementation parser, type checker, interpreter, and command line runner. In this directory, build and test the Bosque reference implementation with:
npm install && npm test

Note: the Z3 theorem prover is provided as a binary dependency in the repo via git LFS. To ensure these are present you will need to have git LFS installed, run

git lfs install
to setup the needed hooks, and pull.

Visual Studio Code Integration

This repository provides basic Visual Studio Code IDE support for the Bosque language (currently limited to syntax and brace highlighting). The installation requires manually copying the full

folder into your user
directory and restarting VSCode.


This project welcomes community contributions.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact [email protected] with any additional questions or comments.

Please refer to Contribution Guidelines for more details.


Code licensed under the MIT License.

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