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Alex Spinov
Alex Spinov

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Flix Has a Free API: The Functional Language With a Built-In Datalog Engine for Program Analysis

#flix #programming #functional #languages

What if your programming language could query its own code like a database? Flix combines functional programming with first-class Datalog constraints, giving you a language where program analysis, type checking, and business rules are built into the syntax.

What Is Flix?

Flix is a functional programming language that runs on the JVM. It combines ML-style type inference, algebraic effects, and a built-in Datalog engine. This means you can write declarative queries over relational data directly in your programs — no external database needed.

Why Flix Is Unique

  • First-class Datalog: Write logic programs alongside functional code
  • Polymorphic effects: Track side effects in the type system
  • Type inference: Hindley-Milner type system with no annotations needed
  • JVM interop: Call Java libraries directly
  • Pattern matching: Exhaustive matching on algebraic data types
  • Completely free and open source

Quick Start

Install Flix:

# Download the compiler
curl -L -o flix.jar https://github.com/flix/flix/releases/latest/download/flix.jar

# Create a new project
java -jar flix.jar init
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Write functional code with Datalog:

// Define relations
rel Edge(x: String, y: String)
rel Path(x: String, y: String)

// Datalog rules — find all paths in a graph
Path(x, y) :- Edge(x, y).
Path(x, z) :- Path(x, y), Edge(y, z).

// Facts
Edge("a", "b").
Edge("b", "c").
Edge("c", "d").

// Query: all nodes reachable from "a"
def main(): Unit \ IO =
    query Path(x, y) from solve Path, Edge
    |> println
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Functional programming features:

// Algebraic data types
enum Shape {
    case Circle(Float64)
    case Rectangle(Float64, Float64)
    case Triangle(Float64, Float64, Float64)
}

// Pattern matching with exhaustiveness checking
def area(s: Shape): Float64 = match s {
    case Shape.Circle(r)           => Float64.pi() * r * r
    case Shape.Rectangle(w, h)     => w * h
    case Shape.Triangle(a, b, c)   =>
        let s1 = (a + b + c) / 2.0;
        Float64.sqrt(s1 * (s1 - a) * (s1 - b) * (s1 - c))
}

// Higher-order functions with type inference
def transform(xs: List[Int32], f: Int32 -> Int32): List[Int32] =
    List.map(f, xs)
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Why Developers Choose Flix

A research team building a static analysis tool tried implementing their analysis in Java. The Datalog-style rules they needed required an external engine and complex integration. With Flix, they wrote the analysis rules directly in Datalog syntax within their Flix program. What took 2,000 lines of Java became 200 lines of Flix.

Who Is This For?

  • PL researchers exploring functional-logic programming
  • Static analysis developers needing Datalog for program queries
  • JVM developers wanting a modern functional language
  • Anyone interested in languages that push programming forward

Try Flix

Flix shows what happens when you combine functional programming with logic programming in one language. If you work with graph analysis, rule engines, or program analysis, Flix might change how you think about these problems.

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