Implement printf, dprintf, string.format

luprex/cpp/core/pprint.hpp

@@ -27,6 +27,7 @@ struct PrettyPrintOptions {
     int level;
     bool expand;
     PrettyPrintOptions() : indent(true), level(0), expand(true) {}
+    PrettyPrintOptions(bool indent, bool expand) : indent(indent), level(0), expand(expand) {}
     void parse(LuaKeywordParser &kp);
 };
 
@@ -42,4 +43,36 @@ void atomic_print(LuaCoreStack &LS, LuaSlot val, bool quote, std::ostream *os);
 //
 void pprint(LuaCoreStack &LS, LuaSlot val, const PrettyPrintOptions &opts, std::ostream *os);
 
+// Format a string using printf-style format specifiers, consuming
+// arguments from a LuaExtraArgs.  Returns an empty string on success,
+// or an error message on failure.
+//
+// Numeric types (argument must be a number).  All of the following
+// use the same formatting parameters as 'printf'.
+//   
+//   %d, %i   — signed decimal integer
+//   %o       — unsigned octal
+//   %u       — unsigned decimal
+//   %x, %X   — unsigned hexadecimal (lower/upper)
+//   %e, %E   — scientific notation (lower/upper)
+//   %f       — decimal floating point
+//   %g, %G   — shortest of %e/%f (lower/upper)
+//   %c       — character (integer converted to character)
+//
+// Non-numeric types:
+//   %s       — prints any lua value using atomic_print (unquoted)
+//   %q       — prints any lua value using atomic_print (quoted)
+//
+// Pretty-printing:
+//
+//   %p       - pretty print
+//   %lp      - pretty print, but all on one line
+//   %P       - pretty print, force table expansion
+//   %lP      - pretty print, force table expansion, all on one line
+//    
+// Special:
+//   %%       — literal percent sign (consumes no argument)
+//
+eng::string format(LuaCoreStack &LS, std::string_view fmt, LuaExtraArgs args, std::ostream *os);
+
 #endif // PPRINT_HPP