Novus

Novus is a general purpose, statically typed, functional programming language. Novus source compiles into instructions for the Novus virtual machine which provides the runtime (eg Garbage collection) and platform abstraction (eg io). The runtime supports Linux, Mac and Windows at this time.

Note: This is intended as an academic exercise and not meant for production projects.

Intro

Novus is an expression based pure functional language with eager evaluation. In practice this means that all types are immutable, normal functions cannot have side-effects and all functions have to produce a value.

Simplest function:

fun square(int x) x * x

Input parameters have to be typed manually but the return type is inferred from the expression.

Advantage of providing type information for the input parameters is that functions can be overloaded:

fun getTxt(string s)  s
fun getTxt(bool b)    b ? "true" : "false"
fun getTxt(User u)    n.name

Expressions can be combined using the group operator ';' (similar to the comma operator in some languages). In an expression group the result is the value of the last expression.

Can be used to define a constant and reuse it in the next expression:

fun cube(int x)
  sqr = x * x; sqr * x

Note: All 'variables' are single assignment only, so in the above example sqr cannot be redefined to mean something else later.

Control flow

Conditional operator

For simple control-flow the conditional-operator (aka ternary-operator) can be used:

fun max(int a, int b)
  a > b ? a : b

Switch expression

For more elaborate control-flow there is the switch expression:

fun fizzbuzz(int i)
  fizz = i % 3 == 0;
  buzz = i % 5 == 0;
  if fizz && buzz -> "FizzBuzz"
  if fizz         -> "Fizz"
  if buzz         -> "Buzz"
  else            -> string(i)

The switch expression is very similar to 'if' statements in imperative languages, however in Novus its an expression so the entire switch has to produce a value of a single type (meaning it has to be exhaustive, so an 'else' is required if the compiler cannot guarantee the if conditions being exhaustive).

Note: there are no loops in Novus, instead iterating is done using recursion. When performing tail recursion the runtime guarantees to execute it in constant stack space.

Type system

The Novus type system contains some basic types build in to the language:

• int (32 bit signed integer)
• long (64 bit signed integer)
• float (32 bit floating point number)
• bool
• string
• char (8 bit unsigned integer)

(Plus a few more niche types: sys_stream, sys_process, function, action, future, lazy and lazy_action).

Note: These are the types the language itself supports, there are however many more types implemented in the standard library.

And can be extended with three kinds of user defined types:

Struct (aka record)

struct User =
  string  name,
  int     age

fun getDefaultUser()
  User("John doe", 32)

fun getName(User u)
  u.name

Union (aka discriminated union or tagged union)

union IntOrBool = int, bool

fun getVal(int i)
  i == 0 ? false : i

fun getNum(IntOrBool ib)
  if ib as int  i -> i
  if ib as bool b -> b ? 1 : 0

Note that there is no 'else' in the last switch expression, this is allowed because the compiler can guarantee that the if conditions are exhaustive.

Enum (aka enumeration)

enum WeekDay =
  Monday    : 1,
  Tuesday   : 2,
  Wednesday : 3,
  Thursday,
  Friday,
  Saturday,
  Sunday

fun sunday()
  WeekDay.Sunday

fun isSunday(WeekDay wd)
  wd == WeekDay.Sunday

Enum's follow the conventions that most c-like languages have, they are named values. If no value is provided the last value is automatically incremented by one (starting from 0).

Generic programming (type and function templates)

To aid in generic programming you can create type and function templates (similar in spirit to c++ templates). Instead of angle brackets '<>' found in many other languages to define a type set, Novus uses curly braces '{}'.

Type template

struct Pair{T1, T2} =
  T1 first,
  T2 second

Instantiation of a type template:

fun sum(float a, float b)
  sum(Pair(a, b))

fun sum(Pair{float, float} p)
  p.first + p.second

Note: When constructing a type the type parameters can be inferred from usage.

Function template

fun sum{T}(T a, T b)
  a + b

fun onePlusTwo()
  sum(1, 2)

Note: When calling a templated function most of the time the type parameters can be inferred.

Operator overloading

Operators can defined like any other function.

struct Pair = int first, int second

fun +(Pair a, Pair b)
  Pair(a.first + b.first, a.second + b.second)

fun [](Pair p, int i)
  i == 0 ? p.first : p.second

fun sum(Pair a, Pair b)
  a + b

fun getFirst(Pair p)
  p[0]

The following list of operators can be overloaded: +, ++, -, --, *, /, %, &, |, !, !!, <<, >>, ^, ~, ==, !=, <, >, <=, >=, ::, [], (), ?, ??.

Note: All operators are left associative except for the :: operator, which makes the :: operator ideal for creating linked lists.

First class functions

Functions can be passed as values using the build-in function{} type template. The last type in the type-set is the return-type, the types before that are the input types.

fun performOp(int val, function{int, int} op)
  op(val)

fun square(int v) v * v
fun cube(int v)   v * v * v

print(performOp(43, cube))
print(performOp(43, square))

Lambda's (aka anonymous functions)

Anonymous functions can be defined using the lambda syntax.

fun performOp(int val, function{int, int} op)
  op(val)

print(performOp(43, lambda (int x) x * x))

Closures

Lamba's can capture variables from the scope they are defined in.

fun performOp(int val, function{int, int} op)
  op(val)

fun makeAdder(int y)
  lambda (int x) x + y

print(performOp(42, makeAdder(1337))

Instance calls

The first argument to a function can optionally be placed in front of the function call. This is syntactic sugar only, but can aid in making function 'chains' easier to read.

fun isEven(int x) (x % 2) == 0
fun square(int x) x * x

print(rangeList(0, 100).filter(isEven).map(square))

Parallel computing

Putting the keyword fork in front of any function call runs it on its own executor (thread) and returns a future{T} handle to the executor.

fun fib(int n)
  n <= 1 ? n : fib(n - 1) + fib(n - 2)

fun calc()
  a = fork fib(25);
  b = fork fib(26);
  a.get() + b.get()

Note this is where a pure functional language shines, its completely safe to run any pure function in parallel without any need for synchronization.

Actions

As mentioned before functions are pure and cannot have any side-effects, but a program without side-effects is not really useful (something about a tree falling in a forest..).

That's why there are special kind of impure functions which are allowed to perform side-effects. Those functions are called 'actions'. An action is allowed to call into a function but not vise versa.

import "std.ns"

act printFile(Path file)
  in  = fileOpen(file, FileMode.Open);
  out = consoleOpen(ConsoleKind.StdOut);
  copy(in, out)

act main()
  print("Which file do you want to print?");
  p = Path(readLine());
  print("Ok, printing: " + p);
  printFile(p)

main()

Note: To pass an action as a value you use the action{} type template instead of the function{} one.

Note: To create an 'action' lambda you can use the impure keyword in front of the lambda: impure lambda (int x) x * x

Try it out

Examples

Several examples can be found in the examples directory.

Docker

You can quickly try it out using docker. Open a interactive container with the compiler, runtime and examples installed: docker run --rm -it bastianblokland/novus sh

Run an example: nove.nx examples/fizzbuzz.ns

Installing the compiler and runtime

At this time there are no releases of binary files, however you can try out the binaries produced by the ci.

The best way is to build the compiler and runtime yourself, the process is documented below.

Building

Requirements

Linux

• CMake (At least version 3.15).

• Modern C++ compiler (at least c++ 17) (Tested with gcc 7.5.0 and clang 9.0.0).

MacOs

• CMake (At least version 3.15).

• Modern C++ compiler (at least c++ 17) (Tested with apple clang 11 and clang 9.0.0).

Windows

• CMake (At least version 3.15).

  For example with chocolatey: choco install cmake.

Building can either be done using MinGW (windows port of Gcc and related tooling) or Visual Studio (msvc).

MinGW

• MinGW-w64. Note: Either version 7.x or 9.x, version 8.x has a broken std::filesystem library impl.

  For example with chocolatey: choco install mingw --version=7.3.0. Unfortunately 9.x is at the time of writing not yet on chocolatey, but the nuwen distribution ships it.

Visual Studio

• Tested with Visual Studio 2019 (make sure the c++ tooling is installed).

• For command-line building install vswhere (https://github.com/microsoft/vswhere).

  For example with chocolatey: choco install vswhere.

Configure

Before building you have to configure the project, run scripts/configure.sh on unix or scripts/configure.ps1 on windows.

For Visual Studio run scripts/configure.ps1 -Gen VS2019, after which the Visual Studio project can be found in the build directory.

On unix run scripts/configure.sh --help for a listing of options, on windows: Help scripts/configure.ps1

Building

After configuring the project can be build by running scripts/build.sh on unix or scripts/build.ps1 on windows.

Build output can be found in the bin directory. For more convenience you can add the bin directory to your PATH.

Building novus source code

Novus source (.ns) can be compiled into an novus executable (.nx) using the novc compiler.

Example: ./bin/novc examples/fizzbuzz.ns. The output can be found at examples/fizzbuzz.nx.

Running novus an executable

An Novus executable (.nx) can be run in the novus runtime (novrt).

Example: ./bin/novrt examples/fizzbuzz.nx.

For more convenience you can also run .nx files without specifying the runtime:

Unix

On unix this can be achieved by adding the runtime to your PATH.

Windows

On Windows you will have to install file associations using ./bin/novrt --install or run the ./bin/novus-install.bat batch script.

That way windows knows to open .nx files with the novrt.exe executable. To uninstall the associations run ./bin/novrt --uninstall or the ./bin/novus-uninstall.bat batch script.

In either case the result is that you can directly run novus executables:

./fizzbuzz.nx

Evaluator

Alternatively you can use the nove.nx (novus evaluator) to combine the compilation and running.

You can either pass the source straight to the evaluator: ./bin/nove.nx 'print(pow(42, 1.337))'.

or give a .ns source file to the evaluator: ./bin/nove.nx examples/fizzbuzz.ns.

Debugging

While there is no debugger (yet?) for novus programs, there are a few diagnostic programs:

• novdiag-prog (Show the generated ast, optionally after optimizing)
• novdiag-asm (Show the generated nov assembly code)
• novdiag-parse (Show the parse-tree output)
• novdiag-lex (Show the output tokens of the lexer)

Testing

After building the project you can run the tests by running scripts/test.sh on unix or scripts/test.ps1 on windows.

Note: To run the compiler and vm tests they have to be enabled and build in the configure step.

Ide

For basic ide support when editing novus source code check the ide directory if there is a plugin for your ide.

For ide support when editing the compiler and vm:

• Configure the project: make configure.debug.
• Copy / symlink the file build/compile_commands.json to the root of the project.
• Use a ide extension for cpp support, for example: clangd (vscode ext: vscode-clangd)

Name

Naming things is hard 😅 From the Stargate tv-show: Novus = 'new' in ancient.