diff --git a/ast/ast.go b/ast/ast.go
index 0661b96..d4a826c 100644
--- a/ast/ast.go
+++ b/ast/ast.go
@@ -89,13 +89,21 @@ func (ast *AST) Pretty() string {
 		for _, elem := range val.Params {
 			agg = append(agg, elem)
 		}
-		opt := ""
+		rest := ""
 		if val.HasRest() {
-			opt = " . " + *val.Rest
+			rest = " . " + *val.Rest
 		}
 		// TODO: opt
+    opt := ""
+		iter := val.Opt.IterFunc()
+		for kv, ok := iter(); ok; kv, ok = iter() {
+      opt += "(o " + kv.Key.(string) + " " + kv.Value.(*AST).Pretty() + ")"
+    }
+    if val.HasOpt() && (val.HasRest() || len(agg) != 0) {
+      opt = " " + opt
+    }
 		body := val.Body.Pretty()
-		return "(fn (" + strings.Join(agg, " ") + opt + ") " + body + ")"
+		return "(fn (" + strings.Join(agg, " ") + rest + opt + ") " + body + ")"
 	} else if ast.Tag == Char {
 		return "#" + string(ast.Val.(rune))
 	} else if ast.Tag == Table {
diff --git a/eval/eval.go b/eval/eval.go
index 9e2e817..a84e35a 100644
--- a/eval/eval.go
+++ b/eval/eval.go
@@ -282,7 +282,7 @@ func evalFn(input []*ast.AST, e ast.Env) (*ast.AST, error) {
 				return nil, fmt.Errorf("Argument list cannot contain %s", a.Pretty())
 			}
 			if argvln == 2 {
-				opt.Set(argv[1].Val.(string), nil)
+				opt.Set(argv[1].Val.(string), &nilVal)
 			} else if argvln == 3 {
 				opt.Set(argv[1].Val.(string), argv[2])
 			}