What is this?

ichiban/prolog is an embeddable ISO Prolog interpreter in Go.

• Standards-compliant:
  • ISO/IEC 13211-1:1995 Information technology — Programming languages — Prolog — Part 1: General core
  • A Prologue for Prolog
  • DCGs
• Easy to integrate: database/sql-like Go API
• Highly customizable:
  • Sandboxing
  • Custom predicates in Go
  • Custom terms (data types) in Go

Comparison with Other Libraries

	prolog	otto	go-lua
Language	ISO Prolog	ECMA Script	Lua
Paradigm	🎓 Logic	Object-oriented	Object-oriented
Go API	😻 database/sql-like	original	original
Declarative	✅	❌	❌
Sandboxing	✅	❌	✅

Getting started

Install latest version

go get -u github.com/ichiban/prolog

Usage

Instantiate an interpreter

p := prolog.New(os.Stdin, os.Stdout) // Or `prolog.New(nil, nil)` if you don't need user_input/user_output.

Or, if you want a sandbox interpreter without any built-in predicates:

// See examples/sandboxing/main.go for details.
p := new(prolog.Interpreter)

Load a Prolog program

if err := p.Exec(`
	human(socrates).       % This is a fact.
	mortal(X) :- human(X). % This is a rule.
`); err != nil {
	panic(err)
}

Similar to database/sql, you can use placeholder ? to insert Go data as Prolog data.

if err := p.Exec(`human(?).`, "socrates"); err != nil { // Same as p.Exec(`human("socrates").`)
	panic(err)
}

Run the Prolog program

sols, err := p.Query(`mortal(?).`, "socrates") // Same as p.Query(`mortal("socrates").`)
if err != nil {
	panic(err)
}
defer sols.Close()

// Iterates over solutions.
for sols.Next() {
	fmt.Printf("Yes.\n") // ==> Yes.
}

// Check if an error occurred while querying.
if err := sols.Err(); err != nil {
	panic(err)
}

Or, if you want to query for the variable values for each solution:

sols, err := p.Query(`mortal(Who).`)
if err != nil {
	panic(err)
}
defer sols.Close()

// Iterates over solutions.
for sols.Next() {
	// Prepare a struct with fields which name corresponds with a variable in the query.
	var s struct {
		Who string
	}
	if err := sols.Scan(&s); err != nil {
		panic(err)
	}
	fmt.Printf("Who = %s\n", s.Who) // ==> Who = socrates
}

// Check if an error occurred while querying.
if err := sols.Err(); err != nil {
	panic(err)
}

The Default Language

ichiban/prolog adheres the ISO standard and comes with the ISO predicates as well as the Prologue for Prolog and DCG predicates.

See the Wiki for the directives and the built-in predicates.

Top Level

1pl is an experimental top level command for testing the default language and its compliance to the ISO standard.

You can install it with go install:

go install github.com/ichiban/prolog/cmd/1pl@latest

Then, you can enter the top level with 1pl:

$(go env GOPATH)/bin/1pl [<file>...]

Extensions

• predicates: Native predicates for ichiban/prolog.
• kagomelog: a Japanese morphological analyzing predicate.

License

Distributed under the MIT license. See LICENSE for more information.

Contributing

See ARCHITECTURE.md for architecture details.

1. Fork it (https://github.com/ichiban/prolog/fork)
2. Create your feature branch (git checkout -b feature/fooBar)
3. Commit your changes (git commit -am 'Add some fooBar')
4. Push to the branch (git push origin feature/fooBar)
5. Create a new Pull Request

Acknowledgments

We would like to extend our thanks to the following individuals for their contributions to this project:

• guregu for contributing code and ideas
• Markus Triska for his deep knowledge and insights on modern Prolog, as evidenced by his insightful comments on issues
• Prof. Ulrich Neumerkel for valuable guidance, his works on ISO standards, the Prologue for Prolog, and DCGs.

We are grateful for the support and contributions of everyone involved in this project. Arigatou gozaimasu!