Re: Decomposition of grammars

[Gavin Wraith <gavin@...>]

In message 
<CACh33Fo+K0Hyvt_xcDVhaM3txYZ+=LO8Ta3EUE+1aTikTOdygQ@mail.gmail.com> 
you wrote:

> Take a look at the Lua Parser on [1]. 
> [1] http://lua-users.org/wiki/LpegRecipes

Thanks. 

> Some other changes you can do to make the code as compact as possible:

I am not too concerned about compactness. More interesting to my mind
is the choice of representation of parse tree that lpeg.match
should return.

Just for reference here is my (no doubt buggy) code - it uses
Peter Shook's patch, '\' for 'function' and '=>' for 'return'. 
The source to be analysed is held in the file named by arg[1].

  #! lua
  -- strip out comments from Lua source
  local S,P,Cg,C,Cmt,Cb,Ct,match in lpeg
  local ret = P "\n"
  
  local shortstring
  local squote, dquote = P "'", P '"'
  do
   local slash, blank = P "\\", ret + " "
   local z = slash*"z"*( blank^0 )
   local esc = slash*(1 - blank)
   local sq = squote*(z + esc + 1 - (squote + slash + ret))^0*squote
   local dq = dquote*(z + esc + 1 - (dquote + slash + ret))^0*dquote
   shortstring = C(sq + dq)
  end
  
  local longstring
  do
   local bra,ket,eqs= P "[",P "]",(P "=")^0
   local open = bra*Cg(eqs,"init")*bra*ret^(-1)
   local close = ket*C(eqs)*ket
   local closeeq = Cmt(close*(Cb "init"),\(s,i,a,b) => a==b end)
   longstring = C(open*((1-closeeq)^0)*close)/(\(s,_) => s end)
  end
  
  local anystring = shortstring + longstring
  
  local strip
  do
   local mm = P "--"
   local comment = mm*(longstring + C((1 - ret)^0))/\(...) => "" end
   local notcomment = (anystring + C(1 - squote - dquote - mm))^1
   strip = Ct((comment + notcomment)^0)/table.concat
  end
  
  local f = io.open(arg[1],"r")
  local s = f:read "*a"
  f:close()
  
  print(strip:match(s))

I think I know what the right mathematical definition of subgrammar
is now. But I do not want to inflict 2-categories on this list ;)
-- 
Gavin Wraith (gavin@wra1th.plus.com)
Home page: http://www.wra1th.plus.com/