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On Tue, 30 Nov 2010 13:37:14 +0200, Tony Finch <dot@dotat.at> wrote:


On Tue, 30 Nov 2010, Juris Kalnins wrote:


 - matching (length, value) encoded strings:
    for example some binary stream, like network packet, that
    at some point stores length, followed by that many bytes.


Use a match-time capture, e.g. for a one-octet count,

  local m = require "lpeg"

  local p = m.Cmt(m.P(1), function (str, pos)
    local len = str:byte(pos)
    return pos+1+len, str:sub(pos+1, pos+len)
  end


Very thanks!



The capture value is a string comprising the len octets following the
count octet.


 - matching output of another lpeg capture.
    for example, some keyword that is case-insensitive.
    can it be matched using P "string" over something?


This might be another job for match-time captures, e.g.

  function kw_pattern(kw)
    return m.Cmt(m.P(#kw), function (str,pos)
      local fin = pos+#kw
      if kw == str:sub(pos,fin):lower()
      then return fin end
    end
  end


Thank you, after fixing the following works:

function kw_pattern(kw)
    return m.Cmt(m.P(#kw), function (str,pos)
        if kw == str:sub(pos-#kw,pos-1):lower() then return true end
    end)
end