Expressions now support function definition

operator-assign.go

@@ -4,8 +4,6 @@
 // operator-assign.go
 package expr
 
-import "fmt"
-
 //-------- assign term
 
 func newAssignTerm(tk *Token) (inst *term) {
@@ -27,12 +25,16 @@ func evalAssign(ctx exprContext, self *term) (v any, err error) {
 
 	leftTerm := self.children[0]
 	if leftTerm.tk.Sym != SymIdentifier {
-		err = fmt.Errorf("left operand of %q must be a variable", self.tk.source)
+		err = leftTerm.tk.Errorf("left operand of %q must be a variable", self.tk.source)
 		return
 	}
 
 	if v, err = self.children[1].compute(ctx); err == nil {
-		ctx.SetValue(leftTerm.tk.source, v)
+		if functor, ok := v.(Functor); ok {
+			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
+		} else {
+			ctx.SetValue(leftTerm.tk.source, v)
+		}
 	}
 	return
 }