active-logic / elk

Behavior tree scripting and interpreters for Unity

ELK and BT-Lang are under development; do not use in production; this repository is shared for early feedback around BT-Lang development; planned alpha: December 2022.

Git URL

[e-mail]:active-logic/elk.git

ELK / BT-lang

This Unity package includes the following:

• BT-Lang ("BTL", pronounced beetle or behtel) is a scripting language for stateless behavior trees
• ELK is a toolkit for quickly building simple interpreters

Requirements

Unity; for now.

• BT-Lang requires Active-Logic or Active-LT
• ELK has no requirements

Get started with BTL

Add your BTL programs under Assets/Resources or any resources directory; the extension is *.txt; the #!btl shebang helps reporting syntax errors (in the Unity console, upon saving your BTL file).

In BTL a behavior tree is a module defining several functions; the entry point is the Step() function.

Sample-BT.txt

#!btl

task Step()
=> Flee(threat!) || DoAttack(target!) || Roam();

task DoAttack(target)
=> Reach(target) && Attack(target) || Face(target);

task Flee(threat)
=> lowHealth && Evade(threat, safetyRange);

task Roam()
=> Move(rdir);

Add a BTL program to a game object via the BTL component.

• 'Path' is the path to the BTL source module, relative to Resources; for example if your BT program is under Resources/Sample.txt, then the path is Sample (without extension)
• Import functions, fields and properties from other components via the BTL component's Import attribute; in the above example, Move and target are external; they are defined in separate components; if name conflict, components higher up the list have priority.
• 'Output' shows the current status of your BT (while running)
• 'Graph' shows the call tree for your BT (while running) along with parameters and return state for every traversed subtask.

The output of the sample program may be something like this:

→ Step()
  ✗ Attack()
    ✗ Reach(null)
  → Roam()
    → Move((-0.99, 0.00, -0.14))

Multiline definitions are supported; multi-statement function definitions are not supported; support for arithmetics (2 + 2) may be dropped; active logic unary/binary ops are supported.

Refer to issues (or file an issue) for planned/available features.

Get started with ELK

ELK will be documented at a later date.