ludic/docs/language/structure/kw-var.md

---

id: kw-var name: var category: structure kind: keyword tokens: var sig: var name: T = value tip: A mutable binding — at program scope, your game's persistent named state. order: 6

A var declares a mutable binding: unlike let, you may reassign it later with =, +=, -=, and friends. Where it appears decides its lifetime — inside a handler or function body it is a local, and at program scope it is persistent, named game state that every handler shares. Program-scope vars are the modern replacement for numeric registers: instead of reg(0), you write var score: int = 0 and read and write score by name. Use var for anything that genuinely changes — accumulators, the current score, a mode flag, an elapsed-frame counter — and prefer let for values that never change.

program Scorekeeper {
  state ScorekeeperState {
    score: int = 0
    elapsed_frames: int = 0
  }

  handler Tick(scorekeeper_st: mut ScorekeeperState) phase Update {
    scorekeeper_st.elapsed_frames = scorekeeper_st.elapsed_frames + 1
    if scorekeeper_st.elapsed_frames % 60 == 0 { scorekeeper_st.score = scorekeeper_st.score + 1 }
  }

  handler DrawWorld(scorekeeper_st: ScorekeeperState) phase Render {
    Screen.clear(Color.MidnightBlue)
    Screen.draw_text(x: 6, y: 4, text: "SCORE", color: Color.White, scale: 1)
    Screen.draw_number(x: 52, y: 4, value: scorekeeper_st.score, color: Color.Gold, scale: 1)
    Screen.show()
  }
}