A small embedding of logic programming with a simple complete search

Abstract

We present a straightforward, call-by-value embedding of a small logic programming language with a simple complete search. We construct the entire language in 54 lines of Racket---half of which implement unification. We then layer over it, in 43 lines, a reconstruction of an existing logic programming language, miniKanren, and attest to our implementation's pedagogical value. Evidence suggests our combination of expressiveness, concision, and elegance is compelling: since microKanren's release, it has spawned over 50 embeddings in over two dozen host languages, including Go, Haskell, Prolog and Smalltalk.