Re: DSL in lua

[Philipp Janda <siffiejoe@...>]

Am 06.12.2012 06:52, schrieb Vasiliy Tolstov:
> Hello.

Hi!

> What is the best way to create custom DSL in Lua? Google says, that it
> can be possible via base lua or using lpeg.
>
> I need something like this
> direcotry "/etc/" {
>    owner "root"
>    group "wheel"
>    mode "0755"
>    action "create"
> }
>
> Can somebody provie minimal lua code for this sample? How can i do
> this using lua lpeg?

Here is a possible solution using LPeg:
#!/usr/bin/lua

local grammar = require( "grammar" )

local g = grammar.define( function(_ENV)
  local _ = WS^0
  local str_E = (P'"'*C( (ANY-P'"')^0 )*P'"') +
                E"string literal expected"
  local eof = -ANY + E"directory expected"

  startrule( "dsl", _ * (V"directory")^0 * eof )
  rule( "directory", W"directory" * _ * (str_E) * _ *
                     (P"{"+E"{ expected") * _ *
                     (V"owner" + V"group" + V"mode" + V"action")^0 *
                     (P"}"+E"owner|group|mode|action|} expected") * _ )
  rule( "owner", W"owner" * _ * (str_E) * _ )
  rule( "group", W"group" * _ * (str_E) * _ )
  rule( "mode", W"mode" * _ * (str_E) * _ )
  rule( "action", W"action" * _ * (str_E) * _ )
end )


local function test( s )
  local ok, ast = pcall( grammar.parsestring, g, s )
  if ok then
    grammar.dumpast( ast )
  else
    print( ast )
  end
  print( ("#"):rep( 80 ) )
end

test[[
directory "/etc/" {
  owner "root"
  group "wheel"
  mode "0755"
  action "create"
}
]]

test[[
directory "/etc/" {
  owner "root"
  gruop "wheel"
  mode "0755"
  action "create"
}
]]

But it requires my grammar-module[1] (which is still work-in-progress). 
If you want to use it anyway, consider it MIT-licensed.

  [1]: http://lua.siffiejoe.dtdns.net/grammar/grammar.lua

Output is:
{
  id = dsl,  pos = 1
  1 = {
    id = directory,  pos = 1
    1 = /etc/
    2 = {
      id = owner,  pos = 23
      1 = root
    }
    3 = {
      id = group,  pos = 38
      1 = wheel
    }
    4 = {
      id = mode,  pos = 54
      1 = 0755
    }
    5 = {
      id = action,  pos = 68
      1 = create
    }
  }
}
################################################################################
["directory "/etc/" {\n..."]:3: parse error, owner|group|mode|action|} 
expected
  gruop "wheel"
  ^
################################################################################


HTH,
Philipp