gominikanren

gominikarnen is an implementation of miniKanren in Go.

What is miniKanren

miniKanren is an embedded Domain Specific Language for logic programming.

If you are unfamiliar with miniKanren here is a great introduction video by Bodil Stokke:

If you like that, then the book, The Reasoned Schemer, explains logical programming in miniKanren by example.

If you want to delve even deeper, then this implementation is based on a very readable paper, µKanren: A Minimal Functional Core for Relational Programming, that explains the core algorithm of miniKanren.

Installation

First install Go

And then run on the command line

$ go get github.com/awalterschulze/gominikanren

Example

AppendO is a goal that appends the first two input arguments into the third input argument. In this example we use AppendO to get all the combinations that can produce the list (cake & ice d t).

package main

import (
    "github.com/awalterschulze/gominikanren/sexpr/ast"
    "github.com/awalterschulze/gominikanren/micro"
    "github.com/awalterschulze/gominikanren/mini"
)

func main() {
    states := micro.RunGoal(
        -1,
        micro.CallFresh(func(x *ast.SExpr) micro.Goal {
            return micro.CallFresh(func(y *ast.SExpr) micro.Goal {
                return micro.ConjunctionO(
                    // (== ,q (cons ,x ,y))
                    micro.EqualO(
                        ast.Cons(x, ast.Cons(y, nil)),
                        ast.NewVariable("q"),
                    ),
                    // (appendo ,x ,y (cake & ice d t))
                    mini.AppendO(
                        x,
                        y,
                        ast.NewList(
                            ast.NewSymbol("cake"),
                            ast.NewSymbol("&"),
                            ast.NewSymbol("ice"),
                            ast.NewSymbol("d"),
                            ast.NewSymbol("t"),
                        ),
                    ),
                )
            })
        }),
    )
    sexprs := micro.Reify("q", states)
    fmt.Println(ast.NewList(sexprs...).String())
}
//Output:
//(
//  (() (cake & ice d t)) 
//  ((cake) (& ice d t)) 
//  ((cake &) (ice d t)) 
//  ((cake & ice) (d t)) 
//  ((cake & ice d) (t)) 
//  ((cake & ice d t) ())
//)