Re: Predefined labels (Inspired by discussion on: Why do we have ipairs?)

["Joseph Manning" <manning@...>]

On 2014-Jun-27 (Fri) at 05:15 (-0400), Sean Conner wrote:

>>   If you are serious about this, you can remove "while", "repeat", "until",
>> "else", "break" and "for" and replace them all with just "if" and "goto".
>>
>> [ snip ]

Seán,

   Modula-2 and Modula-3 have a powerful and flexible "LOOP" statement:

      LOOP
         <statements>
         END

   which repeatedly performs <statements> until explicitly terminated
   by an EXIT statement.

   Both "while" and "repeat" can be realised in the very obvious way
   ( now using lower-case keywords as in Lua, and "break" for "EXIT" ):

      while <condition> do
         <statements>
         end

   is now

      loop
         if not <condition> then break end
         <statements>
         end

   and

      repeat
         <statements>
         until <condition>

   is now

      loop
         <statements>
         if <condition> then break end
         end

   However, whereas "while" / "repeat" allow only a single <condition>,
   and then only at the start / end of the iteration, "loop" allows any
   number of <condition>s, which can occur anywhere in the iteration.

   It's especially useful for "n-and-a-half" type iterations, such as
   reading and processing items until a sentinel is reached, but not
   processing the sentinel itself ( messy with "while" / "repeat" ).

   Moreover, the whole problem with "continue" does not appear to arise
   with the "loop" statement.

   Yes, of course "loop" can be realised with "while true do", but the
   latter form seems a bit ugly, to my eyes.

Joseph

------------------------------------------------------------------------
Joseph Manning / Computer Science / UCC Cork Ireland / manning@cs.ucc.ie
------------------------------------------------------------------------