scryer-prolog/README.md

rusty-wam

The beginnings of the Warren Abstract Machine in Rust, according to the progression of languages in Warren's Abstract Machine: A Tutorial Reconstruction, ending in pure Prolog.

Progress

The language L0 is implemented as a simple REPL. It supports unification on facts and queries without backtracking and rules without clauses, in the familiar Prolog syntax. No data types apart from atoms are currently supported.

An example of the level of interaction currently supported is:

l0> p(Z, Z).  
Program stored.  
l0> ?- p(Z, Z).  
yes  
l0> ?- p(Z, z).  
yes  
l0> ?- p(Z, w).  
yes  
l0> ?- p(z, w).  
no  
l0> ?- p(w, w).  
yes  
l0> ?- p(Z, h(Z, W), f(W)).  
no  
l0> p(Z, h(Z, W), f(W)).  
Program stored.  
l0> ?- p(z, h(z, z), f(w)).  
no  
l0> ?- p(z, h(z, w), f(w)).  
yes  
l0> ?- p(Z, h(z, W), f(w)).  
yes  
l0> ?- p(z, h(Z, w), f(w)).  
yes  
l0> quit

Occurs check

There's no occurs check, so cyclic terms do unify:

l0> p(W, W).
Program stored.
l0> ?- p(f(f(W)), W).
yes