Combinatorial programming with functions
Jo Devriendt
ManyWorlds in a nutshell
Extremely accessible language
With blistering propagation performance
To solve combinatorial problems
Accessible language
3 core ideas
First-class functions
Everything must be finite
bool, int, string primitive types
Online editor @ manyworlds.site
declare S,E,N,D,M,O,R,Y: -> {0..9}.
1000*S() + 100*E() + 10*N() + D()
+ 1000*M() + 100*O() + 10*R() + E()
//---------------------------------------------
= 10000*M() + 1000*O() + 100*N() + 10*E() + Y().
M() > 0.
distinct(S(),E(),N(),D(),M(),O(),R(),Y()).Accessible language
declare some 0-arity functions
function that takes arbitrary number of arguments
My mother can understand this. Yours too! :p
write constraints using normal operators
functions
Accessible language
= != > < >= =< + - * / %
not and or xor implies
abs min max count
distinct same if-then-else
Strongly typed and total along bool, int, string
to-do
overloading for multiple types
Builtin functions
Accessible language
declare <name>: <type>, <type>, ... -> <finite range>.
User functions
declare prime: int -> {true, false}.
declare distance: string, string -> {0..1000}.
declare cities: string -> bool.
declare state: int -> {"busy", "ready", "down"}.
declare edge_color: string, string -> {"r", "g", "b"}.
signature
all ranges have a clear type, but are finite no int or string
declare n: -> {0..9}.
Accessible language
declare color: string -> {"r", "g", "b", "y"}.
color("NL") != color("BE").
color("NL") != color("DE").
color("BE") != color("LU").
color("BE") != color("DE").
color("BE") != color("FR").
color("FR") != color("LU").
color("FR") != color("DE").
color("LU") != color("DE").Map coloring 1
There must be a better way...
Accessible language
declare color: string -> {"r", "g", "b", "y"}.
declare border: string, string -> bool.
define border as {("NL","BE"), ("NL","DE"),
("BE","LU"), ("BE","DE"), ("BE","FR"),
("FR","LU"), ("FR","DE"), ("LU","DE")} else false.
all [ color(x)!=color(y) for x,y where border(x,y) ].Map coloring 2
definition fixes meaning of function
FMF expression
total definition
compiling / flattening / unrolling / grounding / instantiating
yields previous disequalities
Accessible language
FMF expressions
max(f(1), f(2), f(3))all
any
none
count
sum
product
min
max
distinct
same
odd
evenand
or
not( or )
count
+
*
min
max
distinct
same
xor
not( xor )max [ f(x) for x where x in {1..3} ]FMF
corresponding
n-ary function
"scoped builtins"
Accessible language
all [ color(x)!=color(y) for x,y where border(x,y) ].FMF expressions
Filter: select all x,y where border(x,y) holds
Fold: reduce those color(x)!=color(y) to true iff all are true
Map: map those x,y to color(x)!=color(y)
Accessible language
all [ color(x)!=color(y) for x,y where border(x,y) ].FMF expressions
list comprehension
aggregate function converting list to one expression
Accessible language
FMF expressions
Flexible!
sum [
weight(x)
for x where Item(x) and inKnapsack(x)
] <= capacity().Captures global constraints and global functions.
distinct [
color(x)
for x where Country(x) and not color(x)="r"
]."allDiff except 0"
Accessible language
decdef num as {1..9}.
declare cell: int,int -> num.
all [
distinct [ cell(r,c) for c where num(c) ]
for r where num(r) ].
all [
distinct [ cell(r,c) for r where num(r) ]
for c where num(c) ].
declare square: int,int,int -> bool.
define square as ...
all [
distinct [ cell(r,c) for r,c where square(r,c,s)]
for s where num(s) ].
define cell as ...FMF can be arbitrarily nested
Sudoku
Accessible language
FMF expressions
Write your own decomposition
Circuit constraint in TSP
decdef City as {"city_" 1..n}.
declare next: string -> City.
declare order: string -> {1..n}.
order("city_1") = 1.
all [ order(next(x)) = order(x) + 1
for x where City(x) and next(x) != "city_1" ].Accessible language
decdef City as {"city_" 1..n}.
declare next: string -> City.
declare order: string -> {1..n}.
order("city_1") = 1.
all [ order(next(x)) = order(x) + 1
for x where City(x) and next(x) != "city_1" ].FMF caveat: compiler must derive finite instantiation from "where" block
City limits instantations of x as it is a finite set of strings.
Accessible language
3 core ideas
First-class functions
Everything must be finite
bool, int, string primitive types
Online editor @ manyworlds.site
Solve combinatorial problems
find a consistent world
FOUND WORLD
color as {("DE","b"), ("BE","g"), ("FR","r"), ("LU","y"), ("NL","r")}.
declare color: string -> {"r", "g", "b", "y"}.
declare border: string, string -> bool.
define border as {("NL","BE"), ("NL","DE"),
("BE","LU"), ("BE","DE"), ("BE","FR"),
("FR","LU"), ("FR","DE"), ("LU","DE")} else false.
all [ color(x)!=color(y) for x,y where border(x,y) ].
Solve combinatorial problems
debug no consistent world
FOUND BLOCKERS
Line 9: not color("BE")=color("DE")
Line 9: not color("BE")=color("FR")
Line 9: not color("BE")=color("LU")
Line 9: not color("DE")=color("FR")
Line 9: not color("DE")=color("LU")
Line 9: not color("FR")=color("LU")declare color: string -> {"r", "g", "b", "y"}.
declare border: string, string -> bool.
define border as {("NL","BE"), ("NL","DE"),
("BE","LU"), ("BE","DE"), ("BE","FR"),
("FR","LU"), ("FR","DE"), ("LU","DE")} else false.
all [ color(x)!=color(y) for x,y where border(x,y) ].NL is not involved, as it only borders two other countries
Solve combinatorial problems
optimize over all worlds
minimize sum [ distance(x,next(x)) for x where City(x) ].find a world now returns
- optimal world
- optimal objective value
- "optimization blockers"
Solve combinatorial problems
declare man: string -> bool.
declare mortal: string -> bool.
all [ man(x) implies mortal(x)
for x where
x in {"Socrates","Athens","poison cup","Zeus"}
].
man("Socrates").
not mortal("Zeus").FOUND INTERSECTION
man as {("Socrates",true), ("Zeus",false)}.
mortal as {("Socrates",true), ("Zeus",false)}.intersect all worlds
Solve combinatorial problems
Planned:
count all worlds
find relevant unknowns
Performance
BIG to-do
Goal
Means
- C++
- Exact
- multithreaded propagation
- strong compilation
Fastest "intersect" on the planet
Compilation?
Pipeline
- fix parsing
- desugar
- simplify
- instantiate
- simplify
- unnest 1
- simplify
- merge
- unnest 2
- add constraints to solver
Bad: in each step, full expression tree is rebuilt...
Good: minimal set of compiled constraints
Performance
ManyWorlds in a nutshell
Extremely accessible language
With blistering propagation performance
To solve combinatorial problems
Motivation
Combinatorial programming is simpler than imperative programming. Why are the languages so hard?
Successful when a 12-year old can do their math homework with ManyWorlds and when a lawyer can recognize ManyWorld-encoded laws.
Caveat: no silver bullet!
But simple problems should have simple solutions.
Problem domain description should match code.
Usability
- No order on expressions
- e.g., use a function before you declare it
- Deterministic
- Helpful debug information
- syntax mistakes
- compilation errors
- blockers
- Online editor
- No limit on integer type
- Syntax highlighting (to-do)
- Good documentation and tutorials (... to-do)
- ...
Relation to CPMpy
Both focus on
- ease of use
- flexibility
- solver independence
- explanations
Differences
- library vs system
- expressivity of language
- access to solving technology
Summer 2024:
Stateful ManyWorlds with Python interface. New backend? ;)
Little directionality
sum [ distance(x,next(x)) for x where City(x) ]- order of expressions does not matter
- (almost) no distinction between parameters and variables
- even definitions can be used backwards
declare fib: int -> {0..1e21}.
define fib(x) as
0 if x=0 else
1 if x=1 else
fib(x-1) + fib(x-2)
where x in {0..100} else 0.declare fib: int -> {0..1e21}.
declare a,b: -> {0..10}.
define fib(x) as
a() if x=0 else
b() if x=1 else
fib(x-1) + fib(x-2)
where x in {0..100} else 0.
fib(10)=144.- Website with examples & online editor
manyworlds.site
- Source code (should compile on Linux)
gitlab.com/nonfiction-software/manyworlds
(Antlr4 grammar)
- Precompiled docker image
hub.docker.com/r/nonfictionsoftware/manyworlds
- Work-in-progress user documentation
gitlab.com/nonfiction-software/manyworlds/-/wikis/Syntax-and-semantics
- These slides: slides.com/jod/manyworlds-functions
Thanks for your attention!