Creating and Analyzing!
Playable Narratives!
with Linear Logic
Chris Martens
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Graphics Lab, CMU
April 21, 2015
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Creating and Analyzing!
Playable Narratives!
with Linear Logic
Chris Martens
2
Graphics Lab, CMU
April 21, 2015
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Parable of the Polygons (Vi Hart and Nicky Case)
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Causal Understanding
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Outline:
!
1. Background: forms of narrative play
2. Extended example: Shakespeare World
3. Ongoing work: playable specifications
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1. FORMS OF NARRATIVE PLAY
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branching stories
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branching stories
Twine (twinery.org)
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Sam Kabo Ashwell: “Standard Patterns in Choice-Based
Games"
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Sam Kabo Ashwell: “Standard Patterns in Choice-Based
Games"
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branching stories with state
foyer:
(set:$key = true) You found a key!
[[den]]
!
den:
(if: not $key)[There is a cabinet here, but you can't open it.]
(else: )[There's a cabinet here. [[open it]] ]
[[foyer]]
!
open it:
yay cabinet!
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What’s the structure of a stateful story?
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JRWRIR\HU
RSHQFDELQHW
JRWRGHQ
NH\ IR\HU
ZLQ
GHQ
Petri Net
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JRWRIR\HU
RSHQFDELQHW
JRWRGHQ
NH\ IR\HU
ZLQ
GHQ
permanent
states
Petri Net
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JRWRIR\HU
RSHQFDELQHW
JRWRGHQ
NH\ IR\HU
ZLQ
GHQ
Petri Net
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JRWRIR\HU
RSHQFDELQHW
JRWRGHQ
NH\ IR\HU
ZLQ
GHQ
Petri Net
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JRWRIR\HU
RSHQFDELQHW
JRWRGHQ
NH\ IR\HU
ZLQ
GHQ
Petri Net
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JRWRIR\HU
RSHQFDELQHW
JRWRGHQ
NH\ IR\HU
ZLQ
GHQ
choice between
actions
Petri Net
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JRWRIR\HU
RSHQFDELQHW
JRWRGHQ
NH\ IR\HU
ZLQ
GHQ
Petri Net
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aka
“character-driven”
“emergent”
“combinatorial”
COMPOSITIONAL NARRATIVE
One rule might be applied several times, each in a different
narrative state.
!
Thus: rules must be parametric over narrative states!
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COMPOSITIONAL NARRATIVE
Research question:
How can we provide computational support to authoring,
understanding the structure of,
and playing with compositional narratives?
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COMPOSITIONAL NARRATIVE
Answer in progress:
programming language(s) based on linear logic.
Research question:
How can we provide computational support to authoring,
understanding the structure of,
and playing with compositional narratives?
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Outline:
!
1. Background: forms of narrative play
2. Extended example: Shakespeare World
3. Ongoing work: playable specifications
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II. EXTENDED EXAMPLE:
SHAKESPEAREAN TRAGEDY
STORY WORLD
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at
has
anger
affection
depressed
dead
World state:
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insult:
➡️
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do/insult : !
at Alice L * at Eliza L
* anger Alice Eliza!
-o !
at Alice L * at Eliza L
* anger Alice Eliza
* anger Eliza Alice
* depressed Eliza.!
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do/insult : !
$at Alice L * $at Eliza L
* $anger Alice Eliza!
-o !
anger Eliza Alice
* depressed Eliza.!
(notation: $ for resources we want to keep)
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do/insult : !
$at C L * $at C’ L
* $anger C C’!
-o anger C’ C
* depressed C’.!
for all C, C’, L
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do/insult : !
$at C L * $at C’ L
* $anger C C’!
-o anger C’ C
* depressed C’.!
for all C, C’, L
Logic Programming!
(aka Relational Programming)
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Main idea of this section:
Use linear logic programming
(computation = proof search)
to generate narratives over a
space specified by rules.
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compliment:
➡️
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➡️
travel_toward:
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murder:
!
!
➡️
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loot:
➡️
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initial state
!adjacent mon_house town.!
!adjacent town mon_house.!
!adjacent cap_house town.!
!adjacent town cap_house.!
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Program Execution
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A -o B
Δ, A → Δ, B
Δ = arbitrary context of resources A1, …, An
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6 6¶
6R6¶
U 6R6¶
Q
/RJLF3URJUDP
LQLWLDOVWDWH
Program execution in CLF (Watkins et al. 2002)
as realized by Celf (Schack-Nielsen & Schürmann 2008)
quiescence
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Program Execution
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At the end we get:
!
Δ , the final context
!
a trace of rules applied (sequence of narrative actions,
AKA story!)
n
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program traces are!
causally-structured stories
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Outline:
!
1. Background: forms of narrative play
2. Extended example: Shakespeare World
3. Ongoing work: playable specifications
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3. ONGOING WORK:
PLAYABLE SPECIFICATIONS
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accessible tools for making
games
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PuzzleScript
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Horizontal [ > Player | No Obstacle ] ->
[ PlayerBodyH | PlayerHead1 ] sfx2
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Idea:
Replace nondeterminism in the system
with human interactor choice.
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move/up/red : move up * at L (player_head red)
-o at L (player_head red).
!
move/up : move up * at L (player_head C) * next C C'
* adj L up L' * empty L' -o
-o at L player_body * at L' (player_head L’).
!
move/r : move right * at L (player_head C) * adj L right L'
* empty L'
-o at L player_body * at L' (player_head lime).
!
move/l : move left * at L (player_head C) * adj L left L'
* empty L'
-o at L player_body * at L' (player_head lime).
!
% gravity
gravity : at L (player_head C) * adj L down L' * empty L'
-o at L player_body * at L' (player_head C).
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move/up/red : move up * at L (player_head red)
-o at L (player_head red).
!
move/up : move up * at L (player_head C) * next C C'
* adj L up L' * empty L' -o
-o at L player_body * at L' (player_head L’).
!
move/r : move right * at L (player_head C) * adj L right L'
* empty L'
-o at L player_body * at L' (player_head lime).
!
move/l : move left * at L (player_head C) * adj L left L'
* empty L'
-o at L player_body * at L' (player_head lime).
!
% gravity
gravity : at L (player_head C) * adj L down L' * empty L'
-o at L player_body * at L' (player_head C).
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CEPTRE
3 additions to the core language:
!
sensing predicates
acting predicates
stages
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targeted applications:
!
1. game design: easily combine rules from many domains;
invent new mechanics and game logics
!
2. distributed algorithms & systems: easily prototype and
experiment with local rules and their global behavior
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ONGOING/FUTURE WORK
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language implementation
https://github.com/chrisamaphone/interactive-lp
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emergent systems have lots of corner cases
=>
bugs!
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Reasoning Tools
!
1. Statistical analysis of sets of traces
2. Invariant, precondition, and postcondition checking for
stages (static or dynamic)
3. Exhaustive analysis (model checking) for certain
fragments of the language?
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Reasoning Tools
!
1. Statistical analysis of sets of traces
2. Invariant, precondition, and postcondition checking
for stages (static or dynamic)
3. Exhaustive analysis (model checking) for certain
fragments of the language?
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Invariant Checking
Example:
“Whenever the player can reach a locked door, she can
also reach its key.”
!
for all doors D, reachable(player,D)
=> reachable(player, key(D))
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CONCLUSION
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Method:
Linear logic programming + proof theory
!
Results:
1. Structured narrative generation
2. Playable narratives and game sketches
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Takeaway:
!
Programming languages based on logic can bring
rules, narrative, and code into closer alignment,
which aids
prototyping, testing, and reasoning
of compositional simulations.
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Open Q:
!
What is the narrative structure of, say, a classic arcade
game or single-player RPG?
!
Is this structure useful to a designer?
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Hypothesis:
!
Concurrent structure of play traces will not be all that
interesting (modulo independently-acting NPCs)
!
…but Petri Net structure of the rules might be:
feedback loops, “orphan verbs,” resource accumulation
properties, other design features (& bugs)
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Proof search:
!
To run a query
\Delta |- B
!
Seed \Delta_0 = \Delta
Run to quiescence to get \Delta’
Check whether \Delta’ contains everything in B
(and nothing more)
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So for instance I could codify endings in Shakespeare world
like:
!
married A B * dead C -o ending
!
then do a query for
!
init -o ending
!
(in fact this is what I did since Celf doesn’t support traces
for goalless queries!)
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Tamara
Participatory theatre in which participants may follow any
character when they exit a scene
!
Many concurrent + reconverging scenes — concurrent
structure!
!
CLF as dramaturgy tool?