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A tool for buliding JSON-serializable lisps.
Sometimes you need to make something configurable at the database level, but you don't want your application to have to support all possible variations of that configuration.
You can also use Conflisp as a sort of JSON template language, à la Jsonnet.
gem install conflispgem 'conflisp'-
Define your functions
MyLang = Conflisp::Language.define do fn :add, ->(a, b) { a + b } fn :subtract, ->(a, b) { a - b } end
-
Use it
> MyLang.evaluate(['add', 2, ['subtract', 3, 1]]) => 4
You can pass in variables into the evaluator and you will have access to them in your expressions:
> MyLang.evaluate(['add', 2, ['global', 'foo']], globals: { 'foo' => 3 })
=> 5Normally you would store the expressions in a database and then evaluate them when you need to:
> myfoo = MyFoo.find(123)
> configuration = MyLang.evaluate(myfoo.config, globals: { 'current_time' => Time.now.utc })Your functions can also refer to other functions using the resolve method:
MyLang = Conflisp::Language.define do
fn :add, ->(a, b) { a + b }
fn :add_twice, ->(a, b) do
resolve([
'add',
['add', a, b],
['add', a, b]
])
end
endConflisp only provides one built-in function (global). We don't want to be opinionated on the ordering of the arguments to your functions (think lodash vs. lodash/fp), so it is up to the application developer to implement all of their functions.
You can also extend your languages to add new functions:
BaseLang = Conflisp::Language.define do
fn :add, ->(a, b) { a + b }
end
# NewLang will also have access to the `add` method.
NewLang = BaseLang.extend do
fn :foo, ->() do
# ...
end
endMyLang = Conflisp::Language.define do
# Without this we wouldn't be able to express arrays
fn :list, ->(*values) do
values
end
fn :'==', ->(left, right) do
left == right
end
fn :'!=', ->(left, right) do
left != right
end
# Boolean
fn :and, ->(*values) do
raise ArgumentError, 'and requires at least 2 arguments' if values.size < 2
values.reduce do |prev, value|
prev && value
end
end
fn :or, ->(*values) do
raise ArgumentError, 'or requires at least 2 arguments' if values.size < 2
values.reduce do |prev, value|
prev || value
end
end
# Mathematics
fn :'<=', ->(left, right) do
left <= right
end
fn :'>=', ->(left, right) do
left >= right
end
# Collections
fn :dig, ->(collection, *paths) do
collection.dig(*paths)
end
# Special
# This just a wrapper that gives us access to some config passed in through globals
fn :config, ->(*keys) do
resolve(['global', 'config']).dig(*keys)
end
endThen you could run a complex expression like this:
> MyLang.evalute(
[
'join',
' ',
[
'or',
['and', ['>=', ['config', 'current_hour'], 19], 'Good evening'],
['and', ['>=', ['config', 'current_hour'], 13], 'Howdy'],
['and', ['>=', ['config', 'current_hour'], 11], 'Happy noon'],
['and', ['>=', ['config', 'current_hour'], 9], "G'day"],
'Hello'
],
['config', 'user', 'name']
]
globals: {
'config' => {
'current_hour' => Time.now.hour, # 14
'user' => {
'name' => 'Billy'
}
}
}
)
=> "Howdy Billy"When evaluating Conflisp expressions, there are two types of errors that can be raised:
- Conflisp::MethodMissing - raised if a method isn't defined in the language
- Conflisp::RuntimeError - raised if there was an error during evaluation
MIT License
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