Fun With Coroutines

wiki

Print a string in reverse using coroutines

The following example reverses a string. It is implemented with coroutines and recursion (no table).

do

  local wrap, yield = coroutine.wrap, coroutine.yield



  local function putrev(w)

    if w then

      putrev(yield())

      io.write(w)

    end

  end



  function prevchar(s)

    local p = wrap(putrev)

    p"\n"

    string.gsub(s, ".", p)

    p()

  end



  -- don't look at this one until you understand the first one

  function prevword(s)

    local p = wrap(putrev)

    local function q(a, b) p(a) p(b) end

    p"\n"

    string.gsub(s, "(%S+)(%s*)", q)

    p()

  end



end



> prevchar "This is a test" 

tset a si sihT

> prevword "This is a test"

test a is This

> 

-- RiciLake

Control Inversion

Here are two different approaches at control inversion by use of coroutines:

for k in coroutine.wrap(function() table.foreach(_G, coroutine.yield) end) do

  print(k)

end



table.foreach(_G, coroutine.wrap(function(k)

  print(k)

  for k in coroutine.yield do print(k) end

end))

Alas, both don't work with stock Lua. Find out the true reasons why and you will be enlightened. Or just fetch the Coco or RVM extensions and they'll run just fine (see the mailing list for current availability).