World coordinates use (row,column) format, with the row increasing as we move down the screen. We use this format for indexing worlds internally, since it plays nicely with things like drawing the screen, and reading maps from configuration files. The locToCoords and coordsToLoc functions convert back and forth between this type and Location, which is used when presenting coordinates externally to the player.

Convert an external (x,y) location to an internal Coords value.

Convert an internal Coords value to an external (x,y) location.

Represents the top-left and bottom-right coordinates of a bounding rectangle of cells in the world map

A WorldFun t e represents a 2D world with terrain of type t (exactly one per cell) and entities of type e (at most one per cell).

Create a world function from a finite array of specified cells.

A World consists of a WorldFun that specifies the initial world, a cache of loaded square tiles to make lookups faster, and a map storing locations whose entities have changed from their initial values.

Right now the World simply holds on to all the tiles it has ever loaded. Ideally it would use some kind of LRU caching scheme to keep memory usage bounded, but it would be a bit tricky, and in any case it's probably not going to matter much for a while. Once tile loads can trigger robots to spawn, it would also make for some difficult decisions in terms of how to handle respawning.

Load the tile containing a specific cell.

Load all the tiles which overlap the given rectangular region (specified as an upper-left and lower-right corner, inclusive).

Create a new World from a WorldFun.

Look up the terrain value at certain coordinates: try looking it up in the tile cache first, and fall back to running the WorldFun otherwise.

This function does not ensure that the tile containing the given coordinates is loaded. For that, see lookupTerrainM.

Look up the entity at certain coordinates: first, see if it is in the map of locations with changed entities; then try looking it up in the tile cache first; and finally fall back to running the WorldFun.

This function does not ensure that the tile containing the given coordinates is loaded. For that, see lookupEntityM.

Update the entity (or absence thereof) at a certain location, returning an updated World and a Boolean indicating whether the update changed the entity here. See also updateM.

A stateful variant of lookupTerrain, which first loads the tile containing the given coordinates if it is not already loaded, then looks up the terrain value.

A stateful variant of lookupEntity, which first loads the tile containing the given coordinates if it is not already loaded, then looks up the terrain value.

A stateful variant of update, which also ensures the tile containing the given coordinates is loaded.

Enumeration of world updates. This type is used for changes by e.g. the drill command which must be carried out at a later tick. Using a first-order representation (as opposed to e.g. just a World -> World function) allows us to serialize and inspect the updates.