The Boston Diaries

Wednesday, January 25, 2012

99 ways to program a hex, Part 17: Lua, recursion, runtime type checking

Since Lua is a dynamically typed language (“values have types, not variables”) we can check the type of a variable at runtime and behave accordingly. Before, we were restricted with just dumping a file, but we could also dump strings (which in Lua can be pure binary data). So today's version checks what type the input is; if it's a file, we read data from there, otherwise if the input is a string, we pull the next blob of data out of it.

Granted, we don't actually use that feature here, but we can more easily reuse do_dump() elsewhere.

#!/usr/bin/env lua
-- ***************************************************************
--
-- Copyright 2010 by Sean Conner.  All Rights Reserved.
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation, either version 3 of the License, or
-- (at your option) any later version.
--
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-- GNU General Public License for more details.
--
-- You should have received a copy of the GNU General Public License
-- along with this program.  If not, see <http://www.gnu.org/licenses/>.
--
-- Comments, questions and criticisms can be sent to: sean@conman.org
--
-- ********************************************************************

-- Style: Lua 5.1, recursion, runtime type checking

function do_dump(fpin,fpout,offset)
  local line
  
  if type(fpin) == 'string' then
    if offset > string.len(fpin) then return end
    line = fpin:sub(offset + 1,offset + 16)
  else
    line = fpin:read(16)
    if line == nil then return end
  end

  fpout:write(
  	string.format("%08X: ",offset),
  	line:gsub(".",function(c) return string.format("%02X ",c:byte()) end),
  	string.rep(" ",3 * (16 - line:len())),
  	line:gsub("%c","."),
  	"\n"
  )
  return do_dump(fpin,fpout,offset + 16)
end

-- **********************************************************************

if #arg == 0 then
  print("-----stdin-----")
  do_dump(io.stdin,io.stdout,0)
else
  for i = 1 , #arg do
    local f = io.open(arg[1],"r")
    io.stdout:write("-----",arg[1],"-----","\n")
    do_dump(f,io.stdout,0)
    f:close()
  end
end

os.exit(0)

“A big ol' slab of beef!”

Once more into the breach, but I remembered last time this happened, and acted accordingly. But I needn't worry—while we were swarmed with men armed with huge chunks of roast critter, this time, the restaurant was way more crowded and thus, we weren't swarmed quite as heavily.

Also, amusingly, on the far wall from where I was sitting was a large wide screen television showing closeups of grass, of all things. And it wasn't made up like a window either—the grasses would change every so often. And yes, it was video of grass, not static images of grass.

Very odd.

And the food was again, great.

And yes, expense accounts rock!

Wednesday, January 25, 2012

99 ways to program a hex, Part 17: Lua, recursion, runtime type checking

“A big ol' slab of beef!”

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