Re: Most efficient way to recognize a line by its first (up to) three characters

[Frank Meier-Dörnberg <frank@...>]

Am 11.03.2014 20:27, schrieb Luiz Henrique de Figueiredo:
> Bottom line: you need to describe your input precisely. After that, it'll
> be simple to adapt the ideas given in this thread to handle each line.
Putting all above together is fun (and the result may or may not fit):

local function printf(frm, ...)
  print(string.format(frm, ...))
end

local function adapt_handler(prefix_len, LHF_handler)
  return function(line)
     local prefix = line:sub(1,prefix_len)
     local info   = line:sub(prefix_len+1)
     return LHF_handler(prefix, info)
  end
end

local frm = "prefix='%s', info=:'%s'";

local handlers={
    ["A;"]  = function(prefix, info) printf(frm, prefix, info) end,
    ["AB;"] = function(prefix, info) printf(frm, prefix, info) end,
    ["ABC;"]= function(prefix, info) printf(frm, prefix, info) end,
    ["*A "] = function(prefix, info) printf(frm, prefix, info) end,
}

local adapted_handlers = {}
for k,v in pairs(handlers) do
  adapted_handlers[k] = adapt_handler(#k, v)
end

local badprefix=function (line) error("cannot handle "..line) end

example = [[
A;0000;0000;0000
AB;0000;0000;0000
ABC;0000;0000;0000
*A N
]]

for line in example:gmatch("[^\r\n]+") do
  local h =  adapted_handlers[line:sub(1,4)]
          or adapted_handlers[line:sub(1,3)]
          or adapted_handlers[line:sub(1,2)]
          or adapted_handlers[line:sub(1,1)]
          or badprefix
    h(line)
end


Prints out:
prefix='A;', info=:'0000;0000;0000  '
prefix='AB;', info=:'0000;0000;0000'
prefix='ABC;', info=:'0000;0000;0000 '
prefix='*A ', info=:'N'