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https://github.com/sile-typesetter/cassowary.lua
A Lua port of the cassowary constraint solver engine
https://github.com/sile-typesetter/cassowary.lua
cassowary constraints lua luarocks
Last synced: about 2 months ago
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A Lua port of the cassowary constraint solver engine
- Host: GitHub
- URL: https://github.com/sile-typesetter/cassowary.lua
- Owner: sile-typesetter
- License: apache-2.0
- Created: 2014-08-02T20:38:53.000Z (over 10 years ago)
- Default Branch: master
- Last Pushed: 2022-06-16T09:13:40.000Z (over 2 years ago)
- Last Synced: 2024-05-01T22:41:00.693Z (9 months ago)
- Topics: cassowary, constraints, lua, luarocks
- Language: Lua
- Homepage: https://luarocks.org/modules/simoncozens/cassowary
- Size: 146 KB
- Stars: 33
- Watchers: 7
- Forks: 7
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Cassowary
[](https://github.com/sile-typesetter/cassowary.lua/actions?workflow=Luacheck)
[](https://github.com/sile-typesetter/cassowary.lua/actions?workflow=Busted)
[](https://coveralls.io/github/sile-typesetter/cassowary.lua?branch=master)
[](https://github.com/sile-typesetter/cassowary.lua/releases)
[](https://luarocks.org/modules/simoncozens/cassowary)
This is a Lua port of the [cassowary](http://constraints.cs.washington.edu/cassowary/) constraint solving toolkit.
It allows you to use Lua to solve algebraic equations and inequalities and find the values of unknown variables which satisfy those inequalities.
This port is a fairly dumb, bug-for-bug translation of the [Javascript version of cassowary](https://github.com/slightlyoff/cassowary.js).
From that project's description:
> Cassowary and other hierarchial constraint toolkits add a unique mechanism for deciding between sets of rules that might conflict in determining which of a set of possible solutions are "better".
> By allowing constraint authors to specify weights for the constraints, the toolkit can decide in terms of stronger constraints over weaker ones, allowing for more optimal solutions.
> These sorts of situations arise all the time in UI programming; e.g.: "I'd like this to be it's natural width, but only if that's smaller than 600px, and never let it get smaller than 200px".
> Constraint solvers offer a way out of the primordial mess of nasty conditionals and brittle invalidations.
## Getting started
Cassowary.lua is distributed through [LuaRocks](https://luarocks.org/modules/simoncozens/cassowary).
Once installed:
```lua
cassowary = require("cassowary")
-- Create a new solver object
local solver = cassowary.SimplexSolver();
-- Create lua variables to represent x and y
local x = cassowary.Variable({ name = 'x' });
local y = cassowary.Variable({ name = 'y' });
-- Let's encode some expressions:
-- x < y
solver:addConstraint(cassowary.Inequality(x, "<=", y))
-- y = x + 3
solver:addConstraint(cassowary.Equation(y, cassowary.plus(x, 3)))
-- either x = 10 or y = 10
solver:addConstraint(cassowary.Equation(x, 10, cassowary.Strength.weak))
solver:addConstraint(cassowary.Equation(y, 10, cassowary.Strength.weak))
-- The solver automatically tries to resolve the current situation
-- whenever constraints are added, so all we need to do is look
-- at the values:
print("x = "..x.value)
print("y = "..y.value)
```
Depending on the phase of the moon, you will either see:
```
x=7
y=10
```
or
```
x=10
y=13
```
For further examples, see the test suite.
## Licence
This is a derived work of the Javascript port;
I've chosen to licensed it similarly under the Apache 2.0 license.
## Author
Simon Cozens,