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Built‐in Parser

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Doonv edited this page Feb 3, 2024 · 12 revisions

The built-in parser provides a mini-language that can evaluate expressions, call commands, and modify resources. (Entity modification is coming soon, see issue #3)

The built-in parser is enabled by default and can be disabled by disabling the builtin-parser feature.

Important

This guide assumes you already have used Rust before and that you know how it works.

Basic variable assignments and math

For simplicity, the let keyword is not required for creating variables:

$ x = 5 + 4
> 9
$ x - 2
> 7
$ x = x + 3
> 12

Ownership and Borrowing

The built-in parser uses the a similar memory model to Rust's.

This means assigning a variable's value to another causes the original variable to get moved.

$ x = "Hello World!"
> "Hello World!"
$ y = x
> "Hello World!"
$ x
ERROR Variable `x` was moved

For simplicity, references are always mutable, and you can have multiple of them.

You can deference references to modify the value they are references.

$ x = "Hi"
> "Hi"
$ y = &x
> "Hi"
$ z = &x
> "Hi"
$ *z = "Bye"
> "Bye"
$ x
> "Bye"
$ y
> "Bye"

You can also use dereferencing to clone a variable's value.

$ x = "Hmmm"
$ y = *x
$ z = x

Types

Every value can have one of these types:

  • None: The same as () in Rust.
  • Number: Any type of Rust number (You can specify a type like this: 5usize, 2.4f32, 8f64), along with these 2 additional types:
    • Integer: A generic integer of an unknown size that can get downcasted to the appropriate size when used with an integer of a known size.
    • Float: A generic float of an unknown size that can get downcasted to the appropriate size when used with a float of a known size.
  • Boolean: A value that can either be true or false.
  • String: An array of characters, the same as the String type in Rust.
  • Reference: A mutable reference to another value.
  • Object: A dynamic object, equivalent to HashMap<String, Value> in Rust.
  • StructObject: A dynamic object, but with a name. Mostly used for enum assignments.
  • Tuple: A dynamic tuple.
  • StructTuple: A dynamic tuple, but with a name. Mostly used for enum assignments.
  • Resource: A reference to a resource that can be modified.

Native Functions

You can call functions by the name, followed by space seperated arguments.

$ print "Hello World!"
INFO "Hello World!"

Custom native functions can be created and added, see the custom_functions.rs for an example.

Functions/Closures

Coming soon...

Resource Modification

You can modify Resources that implement the Reflect trait by their name.

Warning: Error handling for this is not finished, expect panics.

MyStructResource.number1 = 100
MyEnumResource = Option2
MyEnumResource = StructVariant { a: 5.2, b: "Hi!" }
MyEnumResource = TupleVariant(false)

Entity Queries and Modification

Coming soon...

Loops

Coming soon...

The end, for now

bevy_dev_console is still in active development, and more features will be added soon.

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