Dust

Prototype scripting language WIP

Building

cargo build

Usage

Using variables

You can initialize variables with the let keyword, and optionally annotate their types. If there is no annotation the variable will receive the type of the value on the right hand side.

let x: number = 0

let x, y, z = 0

If the type on the right hand side contradicts the annotated type, then a runtime error will occur.

let x: number = true // Runtime error

Types assigned this way are static and the variable cannot be assigned a value of a different type later on. If you need a dynamic variable whose type can be changed, you must explicitly annotate it with the dyn keyword.

let x: dyn = 1

let x: number, y: dyn = 2

Once a variable is initialized, you can reassing its value with the assignment operator as long as the previously discussed type constraints are satisfied.

x = 42

y = x + 1

The following built-in types are available:

none
number
string
bool

Defining functions

You can define functions using the fn keyword. You must annotate the types of function parameters. Optionally you can also annotate the type of the function's return value.

fn power(base: number, exponent: number) -> number {
    if (exponent == 0) {
      return 1
    }
    return base * power(base, exponent - 1)
}

Built-in Functions:

The following built-in mathematical functions are available: sin, cos, tan, ln, log, abs

For trigonometric functions prepend 'a' for arcus and append 'd' for degree.

Use pi for an accurate value of the constant. For example:

sin(pi)
asind(0.5)

Other built-in functions:

rand(min: number, max: number) -> number
parse_number(input: string) -> number
is_nan(input: number) -> bool
input(prompt: string) -> string
to_string(input: dyn) -> string

Branches

You can use the if keyword with a control expression for conditional execution. If the expression evaluates to false, the block will not run.

The else if keyword allows you to test more conditions only in case the previous ones have evaluated to false.

You can also use the else keyword to specify a block to be executed only in case all of the control expressions evaluated to false.

if x % 2 == 0 {
    println(x)
} else if x < 0 {
    println(-x)
} else {
    println(x + 1)
}

Loops

You can use the while keyword with an expression for conditional loops. The loop will continue to run as long as the expression evaluates to true. Alternatively you can use the break keyword to exit the loop at an arbitrary point.

let x = 0
while x < 10 {
    x = x + 1
    if x == 7 {
        break
    }
}

Printing

You can use the print and println built-in functions to print to the standard output.

let x = 0
while x < 5 {
    println(x * 2)
    x = x + 1
}

Miscellaneous

Supported operators: +, -, /, *, ^, %, <, >, ==, !=, =, and, or, not, typeof
You can use \\ at the end of a line for multiline input.
Input clear to clear the screen.
Input reset to delete all functions and variables.