millieql.md

MilliEQL

A small embeddable query language

MilliEQL is a small query language built for embedding within applications. It supports logic for querying and manipulating data in a simple, typesafe manner.

Motivation

Having a simple query language allows

• Shared frontend / backend logic for form validation or price calculation.
• User-submitted logic
• Cross-language serializable functions

In the past, I've used JSON Logic for such tasks, but JSON logic leaves a bit to be desired:

• It's not very expressive, and even simple things can prove quite annoying to implement
• It doesn't have a dedicated syntax, making reading and writing extremely challenging

In-language usage:

// JavaScript
import millieql from 'millieql';

millieql.query(query, { events: [...] })

# Python
import millieql
millieql.query(query, {"events": [...]})

Example usage:

The following are simple examples of how MilliEQL could be used.

Get count of a specific event

events | filter type="submit" | count

Get count of all event types

events | groupby type | mapvalues count

Get the worst chess line possible.

lines | sort -overallScore | first

Get emails of all users that use the Chat feature

events | filter type="send_message" | groupby email | keys

Get usernames of all users who purchased before signing up

events | sort timestamp | groupby email | mapvalues (sequence type == "purchase", type == "signup") | filtervalues count > 0 | keys

Builtin Types

MilliEQL's types correspond closely to JSON types, for interoperability between different languages.

MilliEQL has 4 primitive types:

• string
• number
• null
• boolean

MilliEQL also has 3 complex types:

• Struct
• Array
• Function<T, K>

The interface of MilliEQL is restricted in that functions can neither be provided as data, nor returned as the result of a query -- they exist entirely within MilliEQL

Reference

The following is a reference of the builtin functions of MilliEQL

keys
values
map
filter
mapvalues
filtervalues
mapkeys
filterkeys
groupby
find
index
first
last
summarize
count