src/Pure/Syntax/ast.ML

 (* pretty_ast *)
 
 fun pretty_ast (Constant a) = Pretty.str (quote a)
   | pretty_ast (Variable x) = Pretty.str x
   | pretty_ast (Appl asts) =
-      Pretty.parents "(" ")" (Pretty.breaks (map pretty_ast asts));
+      Pretty.enclose "(" ")" (Pretty.breaks (map pretty_ast asts));
 
 
 (* pprint_ast *)
 
 val pprint_ast = Pretty.pprint o pretty_ast;