A fast, concurrent based scripting language for D.

This project is maintained by Enalye


Grimoire is an embedded language for D applications. You can easily define custom functions and types from D.




An identifier is a name used to identify something like a variable, a function, a type, etc.

It must not be reserved word, it can use any alphanumeric character, lower and upper cases, or underscores be it can’t start with a digit.

Exemple of valid identifiers: _myVariable MyVAR1__23

? and ! are also valid only if they are put at the end of an identifier: empty?

Reserved words

The following are keyword used by the language, they cannot be used as identifier (variables, functions, etc):

use, main, event, func, task, event, do, while, until, if, unless, else, switch, select, case, loop, for, true, false, let, bool, int, float, string, array, object, tuple, chan, break, continue, return, self, kill, killall, yield, as, is, try, catch, raise, new, defer, void, not, and, or, xor.


Comments are text that are entierly ignored by the compiler, they serve as note for you.

// Everything after those 2 slashes is ignore until the end of the line.

Everything between / * and * / are ignored
/* Nested comments works too */


Numbers can either be integers or floating point values.

An integer is defined by digits from 0 to 9. A float is similar but must either:

You can also use underscores _ inside the number (not in front) to make it more readable: 100_000 The underscores won’t be parsed by the compiler.

First Program

Starting with the traditionnal “Hello World” :

main {
  printl("Hello World!");

The code is composed of the keyword main, it’s a special function that indicate the entry point of the script. Then we have a left curly brace { with a right curly brace } some lines after. Those curly braces delimit the scope of the statement (here, the main). Everything inside those curly braces (called a block) will be executed when the main is run. The whole print("Hello World!"); form a single expression terminated by a semicolon.

Then we pass the “Hello World!” string to the print primitive and here is what the output displays: Hello World!.


Main is the starting point of the script, only one main is allowed. It cannot be called except by D.

vm.spawn(); // Call the "main" function

Note: the main {} won’t be specified during this tutorial even when needed to avoid repetitions. All operations (except type definitions and global variables) must exist inside a local scope.

Importing files

You can separate a script between multiple files. To import them, use the use keyword with your file paths.

use "foo/"

// With {} you can specify multiple paths.
use {

The path is relative to the file importing it. Two import with the same absolute path (i.e. the same file) will be included only once.


Variable can store a value that can be used later. A variable is defined by its type and must be declared before use.

int a = 0; Here we created a variable a of type int initialized with the value 0.

If we print the content of a with ‘print(a)’. The prompt will display 0.

A variable must be initialized before accessing its content, else it will raise an error !

Basic Types

They’re only a handful of basic type recognised by grimoire.

Auto Type

let is a special keyword that let the compiler automatically infer the type of a declared variable. Example:

main {
  let a = 3.2; //'a' is inferred to be a float type.

let can only be used on variable declaration and cannot be part of a function signature because it’s not a type !


A variable can either be local or global.


int globalVar; //Declared outside of any scope, accessible everywhere.

main {
  int localVar; //Declared inside the main, only accessible within the main.

Declaration List

You can also declare multiple variables at once separating each identifier with a comma. int a, b;

Initialization will be done in the same order: int a, b = 2, 3; Here a = 2 and b = 3.

If there is not enough values to assign, the other variable will be assigned the last value: int a, b, c = 2, 3; Here a = 2, b = 3, c = 3.

You can skip one or more values by leaving a blank comma, it’ll then copy the last value:

int a, b, c = 12,, 5; Both a and b are equal to 12 while c is equal to 5.

int a, b, c, d = 12,,, 5; Both a, b, and c are equal to 12 while c is equal to 5.

The first value cannot be blank, you cannot do this: int a, b, c = , 5, 2;

Every variable on the same initialization list must be of the same type. Ex: int a, b = 2, "Hi" will raise an error because b is expected to be int and you are passing a string.

But you can use let to initialize automatically different types : let a, b, c, d = 1, 2.3, "Hi!"; Here:

Type casting

You can explicitly cast a value to any type with the keyword as, it must be followed by the desired type like this: float a = 5 as float;.

Custom casting

You can define your own cast by naming a function with as. It must only have one input and one output.

object Obj {}

main {
    let obj = new Obj;
    printl(obj as string); // Prints "Hello"

func as(Obj a) string {
    return "Hello";

Note that if a default convertion exist, it’ll call that instead, so overloading a + operator between 2 ints is useless.

In D

To define a new cast, add it to the GrData.

data.addCast(&myCast, "myObj", myObjType, grString);

Then, define the function itself:

void myCast(GrCall call) {
    auto myObj = call.getObject("myObj");


Much like custom convertions, you can define your own operators. The name of the function must be operator followed by the operation. You also have to respect the number of input the operator uses (1 or 2).

main {
    printl(3.5 + 2);

func operator+(float a, int b) float {
    return a + b as float;

In D

Like addCast, but using addOperator instead.

data.addOperator(&myOperator, "+", ["a", "b"], [grFloat, grInt], grFloat);

Then writing the function itself.

void myOperator(GrCall call) {
    call.setFloat(call.getFloat("a") + cast(int) call.getInt("b"));

Control flow


if is a keyword that allows you to runs a portion of code only if its condition is true, “unless” do the opposite. You can combine it with optionals else if or else unless to do the same thing, only if the previous ones aren’t run. Finally you can add an optional else that is run only if others are not run.


main {
	if(5 < 2) {
		//This code won't run because 5 is never less than 2.
		printl("5 is less than 2 !");

	unless(5 < 2) {
		//This one will, because unless do the opposite of if
		//It's the same thing as if(not 5 < 2) {}
		printl("5 is not less than 2...");

Another one:

main {
	let i = 5;
	if(i > 10) {
		printl("i is more than 10");
	else if(i >= 5) {
		printl("i is 5 or more but less than 10");
	else unless(i < 2) {
		printl("i is 2 or more, but less than 5");
	else { //else must always be put at the end of the (if/unless)/else (if/unless)/else serie, but is optional.
		printl("i is 2 or less");

Switch statement

switch let us do comparisons a bit like if, but in a more concise manner.

let i = "Hello";
case() { // Default case if others aren't valid.
	printl("I don't know what he said");
case("Hey") {
	printl("He said hey");
case("Hello") {
	printl("He said hello");

Contrary to if statement, cases can be put in any order, and will check equality between the switch value and each cases value. A case without value is considered to be a default case like the else above, you can only have one maximum per switch statement.

Select statement

A select is syntaxically like a switch, but differs in that it doesn’t do value comparison, it checks each case for an operation that can process whithout blocking.

case( /* channel operation  */ ) {

case() {
	/* run if the one above is blocked */

Each case contains a potentially blocking operation, the first non-blocking operation case is run. The default case is optional, but without one, the select statement is a blocking operation, otherwise the default case will execute if when others are blocked.

case(myValue = <- myChannel) { // Receive operation
	printl("Received " ~ myValue);
case(myOtherChannel <- "Hello") { // Send operation
	printl("Sent Hello");
case() {
	// Run if no one else can run.
	// If it's not present, select will blocking until one of the case is non-blocking.
	printl("Did nothing");


A loop is a structure that can be executed several time, there are two type of loops.

Infinite loops

An infinite loop is as the title imply, see for yourself:

loop {
	printl("Hello !");

This script will prompt “Hello !” infinitely until the process is killed, be cautious with it. You may want to add either a yield or an exit condition.

Finite loops

Finite loops, on the other hand, have a finite number of time they will run. Contrary to the infinite one, they take an int as a parameter, which indicate the number of loops:

loop(10) {
	printl("I loop 10 times !");

This will only print the message 10 times.

You can also specify an iterator, which must be of type int.

loop(i, 10)
	printl(i); // Prints from 0 to 9

// Same as above, but we declare i.
loop(int i, 10)

// Also valid.
loop(let i, 10)

While/Do While

“while” and “do while” are, akin to loops, statements that can execute their code several time. The difference is, they do not have a finite number of loop, instead, they have a condition (like “if” statements).

int i = 0;
while(i < 10) {
	printl(i); // Here, the output is 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
	i ++;

“do while” is the same as “while” but the condition is checked after having run the code one time.

int i = 11;
do { //This is garanteed to run at least once, even if the condition is not met.
	printl(i); //Will print "11"
while(i < 10)


“for” loops are yet another kind of loop that will automatically iterate on an array of values. For instance:

for(i, [1, 2, 3, 4]) {

Here, the for statement will take each value of the array, then assign them to the variable “i” specified.

The variable can be already declared, or declared inside the for statement like this:

int i;
for(i, [1, 2]) {}


for(int i, [1, 2]) {}

If no type is specified, or declared as let, the variable will be automatically declared as var.

The variable type must be convertible from the array’s values, or it will raise a runtime error.


Like any other language, functions behave the same. They are declared like this:

func myFunction() {}

Here, the function myFunction takes no parameter, returns nothing and do nothing, which is boring..

Here is a function that takes 2 int, and returns the sum of them

func add(int a, int b) int {
  return a + b;

The return type is always put after the parenthesis, if there is no return value, you can put void or leave it blank. If there is no return type, you can use return alone to exit the function anywhere.

func foo(int n) {
  if(n == 0) {
    printl("n is equal to 0");
  printl("n is different from 0");

A function can have multiple return values, the types returned must correspond to the signature of the function.

func foo() int, string, bool {
	return 5, "Hello", false;


Task are Grimoire’s implementation of coroutines. They are syntaxically similar to function except from a few points:


task doThing() {

main {

Here, the main will printl 1, spawn the doThing task, printl 2 then yield to the doThing task which will printl 3 then yield again to the main which will printl 4. Then the main will die so the doThing task will resume and printl 5.

To interrupt the flow of execution of the task and let other task continue, you can use the keyword yield. The task will run again after all other tasks have run once.

You can also delete the task with the keyword kill. Also be aware that inside the scope of a task, the keyword return will behave the same as kill.

There is also killall which simply kills all running tasks.

Note: The main is a special case of a task.

Anonymous functions/tasks

You can declare a function or a task inside another function (or task). Like this:

main {
	let f = func() {};
	let t = task() {};

You can also decide to just run it immediately:

main {
	int a = 7;
	int b = func(int c) int {
		return c * 2;
	printl(b); //Prints 14

The type of a function/task is the same as its declaration without the parameters’ name:

main {
	func(int, float) string, int myFunction = func(int a, float b) string, int { return "Hey", 2; };

You can use a global function/task as an anonymous by getting its address. You can do so by using the & operator. The operator & does not require the function type, except when it has no way to know it at compilation time, like when declaring with let.

func square(int i) int {
	return i * i;

main {
	let f1 = &square; //Error, & has no way to know the type at during compilation (square could be overloaded).
	let f2 = &(func(int) int)square; //Valid, an explicit type prevent this problem.
	f2 = &square; //Now valid, because it's now typed by the previous assignment.

	func(int) int f3 = &square; //Error, can't know the type of f3 since f3 doesn't exist at the time of declaration.
	f3 = &square; //Valid, since f3 is already declared with a type.


If you want to refer to the current function, but you’re inside an anonymous function you can’t because the function has no name.

Except self. Self is used to refers to the current function/task/etc even anonymous ones.

It allows you to do things like this anonymous recursive fibonacci:

func(int n) int {
    if(n < 2) return n;
    return self(n - 1) + self(n - 2);

Event functions

Events are like tasks that can only be spawned from D.

They are declared like tasks and can only be global:

event foo(string msg) {

To spawn this one from D:

auto mangledName = grMangleNamedFunction("foo", [grString]);
if(vm.hasEvent(mangledName)) {
    GrContext context = vm.spawnEvent(mangledName);
	context.setString("Hello World!);

Here the process is a little bit special. First, we need to know the mangled name (name + signature) of the event with “grMangleNamedFunction”. Then, we call it. If the event has parameters, you absolutely must push those values to the new context, else the VM will crash.


Array are a collection of a single type of value.

The type of an array is array() with the type of its content inside the parenthesis:

array(int) myCollection = [1, 2, 3];

By default, a new array has the type of its first element. So, [1, 2, 3] will be an array(int).

You can write it explicitly by preceding the array with its type: array(int)[1, 2, 3]

If your new array is empty [], you have to write the type explicitly else compilation will fail: array(string)[].

To access an array element, the array index (from 0) in written between brackets:

let a = [10, 20, 30][1]; //New array, then immediately take the index 1 of [10, 20, 30], which is 20

let b = [[1, 2, 3], [11, 12, 13], [21, 22, 23]]; //New array
let c = b[1][2]; //Here we access the element at index 1 -> [21, 22, 23], the element at index 2 -> 23
let d = b[1, 2]; //Same as above in a nicer syntax

When accessing an array element, you can also modify it:

let a = [11, 12, 13];
a[0] = 9; //a now has [9, 12, 13]

Array and array indexes are passed by references, that mean manipulating array do not make copies.

let a = [1, 2, [3, 4]];
let b = a[2]; //b is now a reference to the 3rd value of a
b[0] = 9;

printl(a); //Prints [1, 2, [9, 4]]

You can concatenate values into an array by using the concatenation operator ~

let a = 1 ~ [2, 3, 4] ~ [5, 6] ~ 7; //a is now [1, 2, 3, 4, 5, 6, 7]


Enumerations (or enum) are a set of named constants defined inside a single type. They can only be compared between them and can’t do any arithmetic operation.


They are declared with the keyword enum:

enum Color {

Likely, you can declare it in D by calling addEnum on your GrData:

data.addEnum("Color", ["red", "green", "blue"]);

Accessing a field

To access a value, just type the name of the enum with the name of the field you want separated with a dot:

main {
	Color myColor =;

	case( "The color is red !":printl;
	case( "The color is green !":printl;
	case( "The color is blue !":printl;


Classes are types that can hold fields of different types.


Declaration is made with the class keyword.

class MyClass {
    int foo;
    string bar;

It is equivalent to :

data.addClass("MyClass", ["foo", "bar"], [grInt, grString]);

In the D side of thing, you declare an object type with addClass to the GrData.


To create an instance of that class (i.e. an object), you use the new keyword followed by the class type.

MyClass obj = new MyClass;

You can create an object in D by using the createObject() method of GrCall. Here’s a little example:

Grimoire code:

main {
    let myObj = createMessage();

It’ll print “Hello World !”.

Accessing a field

To access a field, use the . notation. = 5; = "Hello";

In D, use set and get functions.

void _prim(GrCall call) {
    auto obj = call.getObject("obj");
    obj.setInt("bar", 5);


Channels are a concept that allow synchronised communication between tasks. If you know them from Go, it’s roughly the same.

Channels are created like this:

chan(int) c = chan(int, 5);

Here, we create a channel that will hold up to 5 int values. The size (5) of the channel is optional, by default, it’s 1.

To pass a value around, you need to use the <- operator

let c = chan(int);
c <- 1; //We send the value 1 through the channel
int value = <-c; //We receive the value from the channel

But a send or receive operation is blocking, you can’t do it on the same task.

task foo(chan(int) c) {
main {
	let c = chan(int);
	c <- "Hello World !";

Here, foo will be blocked until something is written on the channel, then it’ll print it.

Type Aliases

A type alias allow types to be named differently, making long signatures shorter.

func square(int i) int {
	return i * i;

type MyFunc = func(int) int;

main {
    MyFunc myFunc = &(MyFunc) square;

You can also declare aliases in D by calling addTypeAlias on your GrData:

data.addTypeAlias("MyInt", grInt);

Error Handling

Error handling in Grimoire is done by raising/catching errors

To raise an error, simply write:

raise "Error";

If you do nothing about it, the entire VM will panic, because the current task does nothing to catch it.

So we should probably catch it:

main {
	try {
		raise "Error";
	catch(e) {
		printl("I caught " ~ e);

And everything is fine.

Deferred statements

Code put inside a defer statement, is garanteed to be executed at the end of the function/task, even if an error is thrown before the end of the scope.

main {
	defer { printl("Inside defer !"); }
	printl("Before defer");
	raise "Error";

Here, the prompt will show “Before defer”, then “Inside defer !”, even if we raise an error before the end of the scope. It’s useful for handling resources that need to be freed.

Custom Primitives

What’s a primitive

In this language, a primitive is a function declared in D accessible from a script. print for instance, is a primitive.

They must be declared before the compilation anb remain unchanged in the VM.

Primitive declaration

To declare your primitive use addPrimitive. This function takes a callback to your primitive, the name which your primitive will be known as in scripts, an array of parameters’ name, the parameters’ type and, optionally, an array of return value types. Exemple:

//A function print that takes a string and returns nothing
data.addPrimitive(&print_a_string, "print", ["value"], [grString]);
//Function mul() that takes 2 floats and returns one.
data.addPrimitive(&multiply, "mul", ["a", "b"], [grFloat, grFloat], [grFloat]);

If you want to multiply 2 things, a better idea is to declare an operator (if it doesn’t already exists for your types):

data.addOperator(&multiply, "*", ["a", "b"], [grFloat, grFloat], grFloat);

An operator declaration only take the name of the operator it surcharges, 1 or 2 parameters, and a single return type.

But if you want to convert from one type to another using a primitive, you can do so with this function:

data.addCast(&cast_float_to_int, "value", grFloat, grInt);

Much simpler, it takes a single parameter and return value.

The primitive itself

The callback takes a GrCall object and return nothing. The GrCall object contains everything you need about the current running context.

It looks like this:

void myPrimitive(GrCall call) {

Here, the primitive takes a float parameter called "value", and prints it, then returns the int value 99. getXXX methods fetch the parameters, they have the same name/type as declared, else it will throw an exception. setXXX methods returns a value on the stack, beware of the order in which you call setXXX functions.