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

[Tom N Harris <telliamed@...>]

On Tuesday, March 11, 2014 08:12:49 PM meino.cramer@gmx.de wrote:
> ...and the problem with examples is, that they are examples only :)
> And I have to sent all variations to completly define what I need
> (which I am not allowed to do, by the way).
> Only to describe another variation:
> 
> *A N
> 

    codetree = {
        ['A'] = { function(str) --[[ handle A ]] end,
            ['AB'] = { function(str) --[[ handle AB ]] end,
                ['ABC'] = function(str) --[[ handle ABC ]] end
            }
        },
        ['*'] = { --[[ no handler for * ]]
            ['*A'] = function(str) print[[ handle *A ]] end
        }
    }

    function handlecode(str)
        local tree = codetree
        for p = 1,#str do
          local code = str:sub(1,p)
          local nextstate = tree[code] or tree[1]
          if type(nextstate) == "function" then -- leaf node
              return nextstate(str)
          elseif type(nextstate) == "table" then -- branch node
              tree = nextstate
          else
              print("Unknown code")
              return
          end
        end
        if tree[1] then
            return tree[1](str)
        else
            print("Unknown code")
        end
    end

You say you're concerned about the memory of a lookup table so if necessary 
you can prune leaves so the leaf functions have to handle multiple codes. And 
of course the tree can be constructed from a simple table of code=function 
pairs.

-- 
tom <telliamed@whoopdedo.org>