feat(logic): add term_to_atom/2 predicate

x/logic/interpreter/registry.go

@@ -118,6 +118,7 @@ var registry = orderedmap.New[string, any](
 		{Key: "eddsa_verify/4", Value: predicate.EDDSAVerify},
 		{Key: "ecdsa_verify/4", Value: predicate.ECDSAVerify},
 		{Key: "string_bytes/3", Value: predicate.StringBytes},
+		{Key: "term_to_atom/2", Value: predicate.TermToAtom},
 	}...),
 )
 

x/logic/predicate/atom.go

@@ -0,0 +1,52 @@
+package predicate
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/axone-protocol/prolog/engine"
+
+	"github.com/axone-protocol/axoned/v10/x/logic/prolog"
+)
+
+// TermToAtom is a predicate that describes Atom as a term that unifies with Term.
+//
+// # Signature
+//
+//	term_to_atom(?Term, ?Atom)
+//
+// where:
+//   - Term is a term that unifies with Atom.
+//   - Atom is an atom.
+//
+// When Atom is instantiated, Atom is parsed and the result unified with Term. If Atom has no valid syntax,
+// a syntax_error exception is raised. Otherwise, Term is “written” on Atom using write_term/2 with the option quoted(true).
+//
+// # Example
+//
+//	# Convert the atom to a term.
+//	- term_to_atom(foo, foo).
+func TermToAtom(vm *engine.VM, term, atom engine.Term, cont engine.Cont, env *engine.Env) *engine.Promise {
+	switch {
+	case prolog.IsGround(term, env):
+		var strBuilder strings.Builder
+		os := engine.NewOutputTextStream(&strBuilder)
+		return engine.WriteTerm(vm, os, term, engine.List(engine.NewAtom("quoted").Apply(prolog.AtomTrue)),
+			func(env *engine.Env) *engine.Promise {
+				return engine.Unify(vm, prolog.StringToAtom(strBuilder.String()), atom, cont, env)
+			}, env)
+	case prolog.IsGround(atom, env):
+		atom, err := prolog.AssertAtom(atom, env)
+		if err != nil {
+			return engine.Error(err)
+		}
+		is := engine.NewInputTextStream(strings.NewReader(fmt.Sprintf("%s.", atom)))
+		parsedAtom := engine.NewVariable()
+		return engine.ReadTerm(vm, is, parsedAtom, engine.List(),
+			func(env *engine.Env) *engine.Promise {
+				return engine.Unify(vm, term, parsedAtom, cont, env)
+			}, env)
+	}
+
+	return engine.Error(engine.InstantiationError(env))
+}