# P020 Text adventure Explore an old house of eight rooms on a grid - go, take, drop and use things, light a lamp for the dark cellar, unlock a door with the key found there - and carry the crown out to the garden to win; a map shows the rooms you know, and a path command finds a route through them by backtracking. EML-P project `projects/text-adventure` in the EML language repo: 4 module(s), entry `main.eml`, terminal UI. There, `eml project run projects/text-adventure` runs it and `eml project verify projects/text-adventure` replays every session under CPython (two hash seeds) and in the interpreter; the site build replays every session in the interpreter again and publishes a session only if its screen matches. Built on verified corpus cases: maze-solver-backtracking (https://efficientnewlanguage.org/cases/116-maze-solver-backtracking/), grid-coordinate-map (https://efficientnewlanguage.org/cases/172-grid-coordinate-map/). ## Sessions ### bad-input - interpreter: byte-equal to the golden Input: ```text dance go go up n north east take take sword drop lamp use key i path cellar path attic path hall path s n w take lamp drop lamp s take key use lamp n take lamp use lamp use lamp s drop lamp take key use key n map quit ``` Screen: ```text An old house. Somewhere inside is a golden crown: carry it out to the garden to win. Type help for the commands. -- Hall -- A wide hall with a stone floor. Doors lead off in every direction. Exits: north (locked), east, south and west. > dance I do not understand that. Type help for the commands. > Type a command, or help. > go Go where? North, east, south or west. > go up Go where? North, east, south or west. > n The door is locked. > north east I do not understand that. Type help for the commands. > take What do you want to take? > take sword There is no sword here. > drop lamp You do not have the lamp. > use key You do not have the key. > i You are carrying nothing. > path cellar You have not been to the Cellar yet. > path attic There is no room called attic. > path hall You are already in the Hall. > path A path to which room? > s -- Garden -- An overgrown garden behind the house, with a gate to the road. Exits: north. > n -- Hall -- A wide hall with a stone floor. Doors lead off in every direction. Exits: north (locked), east, south and west. > w -- Kitchen -- A cold kitchen. Pots hang from hooks above the stove. You see an oil lamp. Exits: north, east and south. > take lamp You take an oil lamp. > drop lamp You drop an oil lamp. > s -- Cellar -- It is pitch dark. You cannot see a thing. Exits: north. > take key It is too dark to see anything here. > use lamp You do not have the lamp. > n -- Kitchen -- A cold kitchen. Pots hang from hooks above the stove. You see an oil lamp. Exits: north, east and south. > take lamp You take an oil lamp. > use lamp You light the lamp. > use lamp The lamp is already lit. > s -- Cellar -- A low cellar that smells of earth. You see an iron key. Exits: north. > drop lamp You drop an oil lamp. > take key You take an iron key. > use key There is nothing here to unlock. > n -- Kitchen -- A cold kitchen. Pots hang from hooks above the stove. Exits: north, east and south. > map ? ? ? Kitchen* Hall ? Cellar Garden (* is where you are; ? is a room you have not seen.) > quit You leave the house without the crown. Bye. ``` ### basic - interpreter: byte-equal to the golden Input: ```text look map w take lamp n take book use book s s take key use lamp take key i path hall n e n use key n take crown s e n map s w s ``` Screen: ```text An old house. Somewhere inside is a golden crown: carry it out to the garden to win. Type help for the commands. -- Hall -- A wide hall with a stone floor. Doors lead off in every direction. Exits: north (locked), east, south and west. > look -- Hall -- A wide hall with a stone floor. Doors lead off in every direction. Exits: north (locked), east, south and west. > map ? ? ? ? Hall* ? ? ? (* is where you are; ? is a room you have not seen.) > w -- Kitchen -- A cold kitchen. Pots hang from hooks above the stove. You see an oil lamp. Exits: north, east and south. > take lamp You take an oil lamp. > n -- Library -- Shelves of dusty books reach up to the ceiling. You see an old book. Exits: south. > take book You take an old book. > use book You open the book. A note in the margin says: the crown is kept in the study, and the study key is kept below the kitchen. > s -- Kitchen -- A cold kitchen. Pots hang from hooks above the stove. Exits: north, east and south. > s -- Cellar -- It is pitch dark. You cannot see a thing. Exits: north. > take key It is too dark to see anything here. > use lamp You light the lamp. -- Cellar -- A low cellar that smells of earth. You see an iron key. Exits: north. > take key You take an iron key. > i You are carrying an oil lamp, an iron key and an old book. > path hall From the Cellar to the Hall: north, then east. > n -- Kitchen -- A cold kitchen. Pots hang from hooks above the stove. Exits: north, east and south. > e -- Hall -- A wide hall with a stone floor. Doors lead off in every direction. Exits: north (locked), east, south and west. > n The door is locked. > use key You unlock the study door with the iron key. > n -- Study -- A quiet study with a heavy oak desk. You see a golden crown. Exits: south. > take crown You take a golden crown. > s -- Hall -- A wide hall with a stone floor. Doors lead off in every direction. Exits: north, east, south and west. > e -- Gallery -- Old portraits watch you from the walls. Exits: north and west. > n -- Tower -- A narrow room at the top of the tower. From its window you can see the whole house. Exits: south. > map Library Study Tower* Kitchen Hall Gallery Cellar Garden (* is where you are; ? is a room you have not seen.) > s -- Gallery -- Old portraits watch you from the walls. Exits: north and west. > w -- Hall -- A wide hall with a stone floor. Doors lead off in every direction. Exits: north, east, south and west. > s -- Garden -- An overgrown garden behind the house, with a gate to the road. Exits: north. You carry the crown out into the garden. You have won, in 13 moves! Bye. ``` ## Modules ### main.eml ```eml # P020 text adventure: explore an old house, find the crown and carry it out # to the garden. Commands are typed as words - go north (or just n), take # lamp, use key - and the game keeps what you carry, where each thing lies, # which doors are locked and which rooms you know. import world import route import text def can_see(here, where, lamp_lit): # A dark room can be seen only with the lit lamp in it. if not world.rooms[here][4]: return True world.thing_named("lamp") => lamp return lamp_lit and (where[lamp] == 0 - 1 or where[lamp] == here) def describe(here, where, locked, lamp_lit): "" ^0 ("-- " + world.rooms[here][0] + " --") ^0 if can_see(here, where, lamp_lit): world.rooms[here][3] ^0 [] => seen for i in [0:len(world.things) - 1]: if where[i] == here: seen + [world.things[i][1]] => seen if len(seen) > 0: ("You see " + text.listed(seen) + ".") ^0 else: "It is pitch dark. You cannot see a thing." ^0 [] => ways for d in world.directions: world.door_from(here, d) => door if door != None: if locked[door[0]]: ways + [d + " (locked)"] => ways else: ways + [d] => ways ("Exits: " + text.listed(ways) + ".") ^0 def direction(word): # The full direction for north/n, east/e, south/s, west/w, or "". for d in world.directions: if word == d or word == d[0:1]: return d return "" def plural(n, word): if n == 1: return "1 " + word return str(n) + " " + word + "s" world.start_room => here [] => where for t in world.things: where + [t[2]] => where [] => locked for d in world.doors: locked + [False] => locked True => locked[world.study_door] [] => visited [] => known for r in world.rooms: visited + [False] => visited known + [False] => known True => visited[here] True => known[here] False => lamp_lit 0 => moves False => won True => playing "An old house. Somewhere inside is a golden crown: carry it out to the garden to win." ^0 "Type help for the commands." ^0 describe(here, where, locked, lamp_lit) while playing: "" ^0 text.words(text.lower(input("> "))) => ws "" => verb "" => rest if len(ws) > 0: ws[0] => verb text.joined(ws[1:len(ws)]) => rest if direction(verb) != "" and rest == "": "go" => verb direction(ws[0]) => rest if verb == "": "Type a command, or help." ^0 elif verb == "go": direction(rest) => d if d == "": "Go where? North, east, south or west." ^0 elif world.door_from(here, d) == None: ("You cannot go " + d + " from here.") ^0 elif locked[world.door_from(here, d)[0]]: "The door is locked." ^0 else: world.door_from(here, d)[1] => here moves + 1 => moves True => visited[here] True => known[here] if world.rooms[here][0] == "Tower": for i in [0:len(known) - 1]: True => known[i] describe(here, where, locked, lamp_lit) if here == world.goal_room and where[world.thing_named("crown")] == 0 - 1: ""^0 ("You carry the crown out into the garden. You have won, in " + plural(moves, "move") + "!") ^0 True => won False => playing elif verb == "look" or verb == "l": describe(here, where, locked, lamp_lit) elif verb == "take" or verb == "get" or verb == "drop" or verb == "use": 0 - 1 => t if rest != "": text.words(rest) => names world.thing_named(names[len(names) - 1]) => t if rest == "": ("What do you want to " + verb + "?") ^0 elif verb == "take" or verb == "get": if not can_see(here, where, lamp_lit): "It is too dark to see anything here." ^0 elif t == 0 - 1 or where[t] != here: ("There is no " + rest + " here.") ^0 else: 0 - 1 => where[t] ("You take " + world.things[t][1] + ".") ^0 elif t == 0 - 1 or where[t] != 0 - 1: ("You do not have the " + rest + ".") ^0 elif verb == "drop": here => where[t] ("You drop " + world.things[t][1] + ".") ^0 elif world.things[t][0] == "lamp": if lamp_lit: "The lamp is already lit." ^0 else: True => lamp_lit "You light the lamp." ^0 if world.rooms[here][4]: describe(here, where, locked, lamp_lit) elif world.things[t][0] == "key": if world.doors[world.study_door][0] != here: "There is nothing here to unlock." ^0 elif locked[world.study_door]: False => locked[world.study_door] "You unlock the study door with the iron key." ^0 else: "The study door is already unlocked." ^0 elif world.things[t][0] == "book": "You open the book. A note in the margin says: the crown is kept in the study, and the study key is kept below the kitchen." ^0 else: "It is too precious to wear. Carry it out to the garden." ^0 elif verb == "inventory" or verb == "i": [] => mine for i in [0:len(world.things) - 1]: if where[i] == 0 - 1: mine + [world.things[i][1]] => mine if len(mine) == 0: "You are carrying nothing." ^0 else: ("You are carrying " + text.listed(mine) + ".") ^0 elif verb == "map": for line in route.map_lines(here, known): line ^0 "(* is where you are; ? is a room you have not seen.)" ^0 elif verb == "path": 0 - 1 => goal for i in [0:len(world.rooms) - 1]: if text.lower(world.rooms[i][0]) == rest: i => goal if rest == "": "A path to which room?" ^0 elif goal == 0 - 1: ("There is no room called " + rest + ".") ^0 elif goal == here: ("You are already in the " + world.rooms[here][0] + ".") ^0 elif not visited[goal]: ("You have not been to the " + world.rooms[goal][0] + " yet.") ^0 else: route.route(here, goal, locked, visited) => steps if steps == None: "There is no way there through the rooms you have been in." ^0 else: "" => line for i in [0:len(steps) - 1]: if i > 0: line + ", then " => line line + steps[i] => line ("From the " + world.rooms[here][0] + " to the " + world.rooms[goal][0] + ": " + line + ".") ^0 elif verb == "help": "Commands: look, go north/east/south/west (or n, e, s, w), take, drop and use a thing," ^0 "inventory (i), map, path to a room you have been in (path kitchen), quit." ^0 elif verb == "quit": "You leave the house without the crown." ^0 False => playing else: "I do not understand that. Type help for the commands." ^0 "Bye." ^0 ``` Python projection of main.eml: ```python import world import route import text def can_see(here, where, lamp_lit): if not world.rooms[here][4]: return True lamp = world.thing_named("lamp") return lamp_lit and (where[lamp] == 0 - 1 or where[lamp] == here) def describe(here, where, locked, lamp_lit): print("") print("-- " + world.rooms[here][0] + " --") if can_see(here, where, lamp_lit): print(world.rooms[here][3]) seen = [] for i in range(0, len(world.things)): if where[i] == here: seen = seen + [world.things[i][1]] if len(seen) > 0: print("You see " + text.listed(seen) + ".") else: print("It is pitch dark. You cannot see a thing.") ways = [] for d in world.directions: door = world.door_from(here, d) if door != None: if locked[door[0]]: ways = ways + [d + " (locked)"] else: ways = ways + [d] print("Exits: " + text.listed(ways) + ".") def direction(word): for d in world.directions: if word == d or word == d[0:1]: return d return "" def plural(n, word): if n == 1: return "1 " + word return str(n) + " " + word + "s" here = world.start_room where = [] for t in world.things: where = where + [t[2]] locked = [] for d in world.doors: locked = locked + [False] locked[world.study_door] = True visited = [] known = [] for r in world.rooms: visited = visited + [False] known = known + [False] visited[here] = True known[here] = True lamp_lit = False moves = 0 won = False playing = True print("An old house. Somewhere inside is a golden crown: carry it out to the garden to win.") print("Type help for the commands.") describe(here, where, locked, lamp_lit) while playing: print("") ws = text.words(text.lower(input("> "))) verb = "" rest = "" if len(ws) > 0: verb = ws[0] rest = text.joined(ws[1:len(ws)]) if direction(verb) != "" and rest == "": verb = "go" rest = direction(ws[0]) if verb == "": print("Type a command, or help.") elif verb == "go": d = direction(rest) if d == "": print("Go where? North, east, south or west.") elif world.door_from(here, d) == None: print("You cannot go " + d + " from here.") elif locked[world.door_from(here, d)[0]]: print("The door is locked.") else: here = world.door_from(here, d)[1] moves = moves + 1 visited[here] = True known[here] = True if world.rooms[here][0] == "Tower": for i in range(0, len(known)): known[i] = True describe(here, where, locked, lamp_lit) if here == world.goal_room and where[world.thing_named("crown")] == 0 - 1: print("") print("You carry the crown out into the garden. You have won, in " + plural(moves, "move") + "!") won = True playing = False elif verb == "look" or verb == "l": describe(here, where, locked, lamp_lit) elif verb == "take" or verb == "get" or verb == "drop" or verb == "use": t = 0 - 1 if rest != "": names = text.words(rest) t = world.thing_named(names[len(names) - 1]) if rest == "": print("What do you want to " + verb + "?") elif verb == "take" or verb == "get": if not can_see(here, where, lamp_lit): print("It is too dark to see anything here.") elif t == 0 - 1 or where[t] != here: print("There is no " + rest + " here.") else: where[t] = 0 - 1 print("You take " + world.things[t][1] + ".") elif t == 0 - 1 or where[t] != 0 - 1: print("You do not have the " + rest + ".") elif verb == "drop": where[t] = here print("You drop " + world.things[t][1] + ".") elif world.things[t][0] == "lamp": if lamp_lit: print("The lamp is already lit.") else: lamp_lit = True print("You light the lamp.") if world.rooms[here][4]: describe(here, where, locked, lamp_lit) elif world.things[t][0] == "key": if world.doors[world.study_door][0] != here: print("There is nothing here to unlock.") elif locked[world.study_door]: locked[world.study_door] = False print("You unlock the study door with the iron key.") else: print("The study door is already unlocked.") elif world.things[t][0] == "book": print("You open the book. A note in the margin says: the crown is kept in the study, and the study key is kept below the kitchen.") else: print("It is too precious to wear. Carry it out to the garden.") elif verb == "inventory" or verb == "i": mine = [] for i in range(0, len(world.things)): if where[i] == 0 - 1: mine = mine + [world.things[i][1]] if len(mine) == 0: print("You are carrying nothing.") else: print("You are carrying " + text.listed(mine) + ".") elif verb == "map": for line in route.map_lines(here, known): print(line) print("(* is where you are; ? is a room you have not seen.)") elif verb == "path": goal = 0 - 1 for i in range(0, len(world.rooms)): if text.lower(world.rooms[i][0]) == rest: goal = i if rest == "": print("A path to which room?") elif goal == 0 - 1: print("There is no room called " + rest + ".") elif goal == here: print("You are already in the " + world.rooms[here][0] + ".") elif not visited[goal]: print("You have not been to the " + world.rooms[goal][0] + " yet.") else: steps = route.route(here, goal, locked, visited) if steps == None: print("There is no way there through the rooms you have been in.") else: line = "" for i in range(0, len(steps)): if i > 0: line = line + ", then " line = line + steps[i] print("From the " + world.rooms[here][0] + " to the " + world.rooms[goal][0] + ": " + line + ".") elif verb == "help": print("Commands: look, go north/east/south/west (or n, e, s, w), take, drop and use a thing,") print("inventory (i), map, path to a room you have been in (path kitchen), quit.") elif verb == "quit": print("You leave the house without the crown.") playing = False else: print("I do not understand that. Type help for the commands.") print("Bye.") ``` ### world.eml ```eml # P020 text adventure - the house: rooms on a grid, the doors between them, # and the things in it at the start. A room is [name, column, row, # description, dark]; a door is [room, direction, room] and works both ways; # a thing is [name, description, starting room]. [ ["Library", 0, 0, "Shelves of dusty books reach up to the ceiling.", False], ["Study", 1, 0, "A quiet study with a heavy oak desk.", False], ["Tower", 2, 0, "A narrow room at the top of the tower. From its window you can see the whole house.", False], ["Kitchen", 0, 1, "A cold kitchen. Pots hang from hooks above the stove.", False], ["Hall", 1, 1, "A wide hall with a stone floor. Doors lead off in every direction.", False], ["Gallery", 2, 1, "Old portraits watch you from the walls.", False], ["Cellar", 0, 2, "A low cellar that smells of earth.", True], ["Garden", 1, 2, "An overgrown garden behind the house, with a gate to the road.", False], ] => rooms ["north", "east", "south", "west"] => directions [ [4, "north", 1], [4, "west", 3], [4, "east", 5], [4, "south", 7], [3, "north", 0], [3, "south", 6], [5, "north", 2], ] => doors # The door from the hall to the study (door 0) is locked at the start. 0 => study_door [ ["lamp", "an oil lamp", 3], ["key", "an iron key", 6], ["crown", "a golden crown", 1], ["book", "an old book", 0], ] => things 4 => start_room 7 => goal_room def opposite(d): if d == "north": return "south" if d == "south": return "north" if d == "east": return "west" return "east" def door_from(room, d): # [door number, the room it leads to] for the door going d from room, or # None if there is no door that way. for k in [0:len(doors) - 1]: if doors[k][0] == room and doors[k][1] == d: return [k, doors[k][2]] if doors[k][2] == room and opposite(doors[k][1]) == d: return [k, doors[k][0]] return None def room_at(column, row): # The room at a grid position, or -1 if there is none. for i in [0:len(rooms) - 1]: if rooms[i][1] == column and rooms[i][2] == row: return i return 0 - 1 def thing_named(name): # The thing called name, or -1. for i in [0:len(things) - 1]: if things[i][0] == name: return i return 0 - 1 ``` Python projection of world.eml: ```python rooms = [["Library", 0, 0, "Shelves of dusty books reach up to the ceiling.", False], ["Study", 1, 0, "A quiet study with a heavy oak desk.", False], ["Tower", 2, 0, "A narrow room at the top of the tower. From its window you can see the whole house.", False], ["Kitchen", 0, 1, "A cold kitchen. Pots hang from hooks above the stove.", False], ["Hall", 1, 1, "A wide hall with a stone floor. Doors lead off in every direction.", False], ["Gallery", 2, 1, "Old portraits watch you from the walls.", False], ["Cellar", 0, 2, "A low cellar that smells of earth.", True], ["Garden", 1, 2, "An overgrown garden behind the house, with a gate to the road.", False]] directions = ["north", "east", "south", "west"] doors = [[4, "north", 1], [4, "west", 3], [4, "east", 5], [4, "south", 7], [3, "north", 0], [3, "south", 6], [5, "north", 2]] study_door = 0 things = [["lamp", "an oil lamp", 3], ["key", "an iron key", 6], ["crown", "a golden crown", 1], ["book", "an old book", 0]] start_room = 4 goal_room = 7 def opposite(d): if d == "north": return "south" if d == "south": return "north" if d == "east": return "west" return "east" def door_from(room, d): for k in range(0, len(doors)): if doors[k][0] == room and doors[k][1] == d: return [k, doors[k][2]] if doors[k][2] == room and opposite(doors[k][1]) == d: return [k, doors[k][0]] return None def room_at(column, row): for i in range(0, len(rooms)): if rooms[i][1] == column and rooms[i][2] == row: return i return 0 - 1 def thing_named(name): for i in range(0, len(things)): if things[i][0] == name: return i return 0 - 1 ``` ### route.eml ```eml # P020 text adventure - the map of the rooms you know, and a route between # rooms by backtracking: try each open door in turn (north, east, south, # west) into a room you have been in and not yet on this route, go deeper, # and step back when a way leads nowhere. The house has no loops, so the # route found is the only one. import world def search(here, goal, on_route, locked, visited): # The directions from here to goal, or None if there is no way. if here == goal: return [] True => on_route[here] for d in world.directions: world.door_from(here, d) => door if door != None and not locked[door[0]] and visited[door[1]] and not on_route[door[1]]: search(door[1], goal, on_route, locked, visited) => rest if rest != None: return [d] + rest False => on_route[here] return None def route(here, goal, locked, visited): [] => on_route for r in world.rooms: on_route + [False] => on_route return search(here, goal, on_route, locked, visited) def map_lines(here, known): # The house as a grid: a room you know by name (* where you are), one you # do not as ?, and nothing where there is no room. [] => lines for row in [0:2]: " " => line for column in [0:2]: world.room_at(column, row) => r "" => cell if r != 0 - 1 and known[r]: world.rooms[r][0] => cell if r == here: cell + "*" => cell elif r != 0 - 1: "?" => cell line + ("%-10s" % cell) => line len(line) => j while j > 0 and line[j - 1] == " ": j - 1 => j lines + [line[0:j]] => lines return lines ``` Python projection of route.eml: ```python import world def search(here, goal, on_route, locked, visited): if here == goal: return [] on_route[here] = True for d in world.directions: door = world.door_from(here, d) if door != None and not locked[door[0]] and visited[door[1]] and not on_route[door[1]]: rest = search(door[1], goal, on_route, locked, visited) if rest != None: return [d] + rest on_route[here] = False return None def route(here, goal, locked, visited): on_route = [] for r in world.rooms: on_route = on_route + [False] return search(here, goal, on_route, locked, visited) def map_lines(here, known): lines = [] for row in range(0, 3): line = " " for column in range(0, 3): r = world.room_at(column, row) cell = "" if r != 0 - 1 and known[r]: cell = world.rooms[r][0] if r == here: cell = cell + "*" elif r != 0 - 1: cell = "?" line = line + "%-10s" % cell j = len(line) while j > 0 and line[j - 1] == " ": j = j - 1 lines = lines + [line[0:j]] return lines ``` ### text.eml ```eml # P020 text adventure - reading commands. The interpreter that checks every # session does not run string methods yet, so the text handling is written # out here. def lower(s): # s with A-Z turned into a-z; everything else as it was. "ABCDEFGHIJKLMNOPQRSTUVWXYZ" => upper_letters "abcdefghijklmnopqrstuvwxyz" => lower_letters "" => out for c in s: c => d for i in [0:25]: if upper_letters[i] == c: lower_letters[i] => d out + d => out return out def words(s): # The words of s, split at spaces. [] => out "" => word for c in s + " ": if c == " ": if word != "": out + [word] => out "" => word else: word + c => word return out def joined(ws): # Words put back together with single spaces. "" => out for w in ws: if out != "": out + " " => out out + w => out return out def listed(items): # "a lamp", "a lamp and a key", "a lamp, a key and a book". if len(items) == 1: return items[0] "" => out for i in [0:len(items) - 2]: if i > 0: out + ", " => out out + items[i] => out return out + " and " + items[len(items) - 1] ``` Python projection of text.eml: ```python def lower(s): upper_letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" lower_letters = "abcdefghijklmnopqrstuvwxyz" out = "" for c in s: d = c for i in range(0, 26): if upper_letters[i] == c: d = lower_letters[i] out = out + d return out def words(s): out = [] word = "" for c in s + " ": if c == " ": if word != "": out = out + [word] word = "" else: word = word + c return out def joined(ws): out = "" for w in ws: if out != "": out = out + " " out = out + w return out def listed(items): if len(items) == 1: return items[0] out = "" for i in range(0, len(items) - 2+1): if i > 0: out = out + ", " out = out + items[i] return out + " and " + items[len(items) - 1] ``` ## README # P020 - Text adventure A small text adventure in an old house of eight rooms. Somewhere inside is a golden crown; carry it out to the garden to win. Commands are typed as words - go north (or just n), take lamp, use key - and the game keeps what you carry, where each thing lies, which doors are locked and which rooms you know. - `main.eml` - reading commands, the game rules, and the descriptions - `world.eml` - the rooms on a grid, the doors between them, and the things at the start - `route.eml` - the map of the rooms you know, and finding a route between rooms by backtracking - `text.eml` - lower case, words, and lists like "a lamp, a key and a book" The house is a three-by-three grid of positions holding eight rooms, each with a column and a row. The way to the crown takes four things in order: the oil lamp from the kitchen, lit, for the cellar, which is pitch dark without it (a lit lamp lights a room whether you carry it or put it down); the iron key the cellar hides; the key used in the hall to unlock the study door; and the crown, carried out to the garden. The book in the library gives a hint. The game counts your moves. `map` draws the grid with the rooms you have been in by name (* marks where you are) and the others as ?; from the tower you can see the whole house, so the map shows every room after you climb it. `path` finds a way to a room you have been in, through rooms you have been in and doors that are open: it tries each door in turn - north, east, south, west - goes deeper, and steps back when a way leads nowhere. The house has no loops, so the way it finds is the only one, and so the shortest. Commands: look, go north/east/south/west (or n, e, s, w), take (or get), drop and use a thing, inventory (i), map, path to a room, help, quit. Anything else is answered with a hint to type help. Sessions: `sessions/basic.in` plays the whole game - the lamp and the book, the dark cellar lit up, the key, a path back to the hall, the locked study opened, the crown, the tower and its full map - and wins in 13 moves; `sessions/bad-input.in` types an unknown command, nothing, a direction that is not one, a locked door, two directions at once, things that are not there or not carried, paths to rooms that do not exist or are not known yet, walks into the garden without the crown, leaves the lamp behind before the cellar, lights it, puts it down inside the cellar and still sees, tries the key where there is no lock, and quits. Built on the verified corpus cases `maze-solver-backtracking` (a way through a grid found by trying each direction and stepping back) and `grid-coordinate-map` (places kept by their grid coordinates).