Re: [patch] continue statement

[jrs@...]

A little late, but ...

The semantics of continue is available in Lua. No patch required.

while something do
  repeat
    ...
    if expr then break end
    ...
  until true
end

Here 'break' is read as 'goto end of block' ('continue', if you
prefer :-)), and 'repeat ... until true' is read as 'block ... end'.

Some other control structures produced by 'misusing' repeat:

perl's while { ... next ... } continue { ...  }

while something do
  repeat
    ...
    if expr then do break end end
    ...
  until true
  ...           -- the continue block
                -- is always executed just before the
                -- conditional is to be evaluated again.
end


perl's redo and more:

while something do
  ...           -- only runs if not redo
  local redo = false
  repeat
    if redo then
      ...       -- runs only if redo
      redo = false
    end
    repeat
      ...
      -- next line is pronounced 'redo if expr;' :-)
      if expr then redo = true break end
      ...
    until true
    ...         -- runs whether or not redo
  until not redo
  ...           -- continue block doesn't run if redo
end

Whew!   That's enough of that.


The 'goto end of block' can be used to reduce 'if nests' and 'else
thickets', the problem the patch was to solve.  For example,

  if a then
      ...
  else
      ...
      if b then
          ...
      else
          ...       -- code 1 if not a and not b independent of c or d
          if c then
              ...
          else
              ...
              if d then
                 ...
              end
          end
          ...       -- code 2 if not a and not b perhaps dependent on c or d
      end -- some elses in here would make this code even harder to grasp
  end

becomes

  repeat
    if a then
      ...
    else break end
    ...
    if b then
      ...
    else break
    end          -- the traditional placement, easier to read perhaps.
    ...          -- code 1 if not a and not b
    if c then
      ...
    else         -- code 2 may prevent use of break here. perhaps it could
                 -- be here and else could be replaced by 'else break end'
      ...
      if d then
        ...
      end
    end
    ...          -- code 2 here if code under 'if c' or 'if d' does
                 -- influence
  until true

where 'repeat ... until true' is read as 'block ... end fnord:'
and 'else break' is read as 'goto fnord'. :-)

--
jrs