479-atomic.yaml

# See also 479-atomic-race.

version: 1
name: Atomic grab/harvest/place
description: |
  'atomic' blocks should be able to prevent crashes due to race conditions
  https://github.com/swarm-game/swarm/issues/479
stepsPerTick: 1
creative: true
objectives:
  - condition: |
      try {
        p <- robotNamed "planter";
        as p {n <- count "weed"; return (n == 0)}
      } { return false }
solution: |
  def forever = \c. force c ; forever c end
  def tryharvest =
    atomic (
      b <- ishere "weed";
      if b {harvest; return ()} {}
    );
    n <- random 4; wait n
  end;
  forever {tryharvest}
robots:
  - name: base
    loc: [0,0]
    dir: [1,0]
    devices:
      - logger
      - harvester
    inventory:
      - [1, lambda]
  - name: planter
    loc: [0,0]
    dir: [1,0]
    devices:
      - logger
      - grabber
    inventory:
      - [25, weed]
    program: |
      def forever = \c. force c ; forever c end
      def tryplant =
        atomic (
          b <- ishere "weed";
          if b {} {place "weed"}
        )
      end;
      forever {tryplant}
entities:
  - name: weed
    display:
      attr: plant
      char: 'W'
    description:
    - A fast-growing weed.
    properties: [known, portable, growable]
    growth: [1,2]
world:
  palette:
    '.': [grass]
  upperleft: [0,0]
  map: |
    .