[augeas-devel] Inexpressible Language

Thu Jun 26 06:46:09 UTC 2014

Hello,

I'm not sure if you're reporting a bug (in which case it would help to file
it on the bugtracker [0]) or asking for help. I'll suppose the latter.

Here is a lens that parses your example. I suppose there must still be an
issue (which is linked to the restrictions I had to put in the comment
regexp —no "[" allowed as first character— but your example doesn't expose
it then:

===========================
(* foo.aug *)
module Foo =

let eol = del /[ \t]*\n/ "\n"

let empty = [ del /[ \t]*\n/ "\n" ]

let comment =
  let space_in = /[^[ \r\t\n].*[^ \r\t\n]|[^[ \t\n\r]/
  in [ Util.indent . label "#comment" . store space_in . eol ]

let entry =
   let value = [ seq "value" . Sep.colon . store /[^]:]+/ ]
   in [ Util.indent . Util.del_str "["
      . key /[A-Z_]+/ . counter "value" . value+
      . Util.del_str "]" . (comment|eol) ]

let lns = (empty|comment|entry)*

let conf = "Change this to turn sound off.

[SOUND:YES]
[FONT:curses_640x300.png]
[RESIZABLE:YES]You may disable window resizing if you wish.

[PRINT_MODE:2D]
    Mode examples:
[SINGLE_BUFFER:NO]
[EMBARK_RECTANGLE:4:4]

Change these numbers to set the default weights for traffic designations.
 If you make the last numbers too large, pathfinding might lag.
The format is (PATH_COST:<high>:<normal>:<low>:<restricted>).
[PATH_COST:1:2:5:25]\n"

test lns get conf = ?
=====================================
$ augparse foo.aug
Test result: foo.aug:35.0-.21:
  { "#comment" = "Change this to turn sound off." }
  {  }
  { "SOUND"
    { "1" = "YES" }
  }
  { "FONT"
    { "1" = "curses_640x300.png" }
  }
  { "RESIZABLE"
    { "1" = "YES" }
    { "#comment" = "You may disable window resizing if you wish." }
  }
  {  }
  { "PRINT_MODE"
    { "1" = "2D" }
  }
  { "#comment" = "Mode examples:" }
  { "SINGLE_BUFFER"
    { "1" = "NO" }
  }
  { "EMBARK_RECTANGLE"
    { "1" = "4" }
    { "2" = "4" }
  }
  {  }
  { "#comment" = "Change these numbers to set the default weights for
traffic designations.  If you make the last numbers too large, pathfinding
might lag." }
  { "#comment" = "The format is
(PATH_COST:<high>:<normal>:<low>:<restricted>)." }
  { "PATH_COST"
    { "1" = "1" }
    { "2" = "2" }
    { "3" = "5" }
    { "4" = "25" }
  }

Regards,

[0] https://github.com/hercules-team/augeas/issues

On Thu, Jun 26, 2014 at 6:50 AM, Yclept Nemo <orbisvicis at gmail.com> wrote:

> The following language ([1], example), as far as I can tell, is unable to
> be meaningfully represented within Augeas (pardon the possibly horrendous
> syntax, as I'm new to Augeaus):
>
>     let br_l        = del /\[/ "["
>     let br_r        = del /\]/ "]"
>     let ws          = del /[ \t]*/ ""
>     let sep         = del /:/ ":"
>     let comment     = del /.*/ ""
>     let eol         = del /\n/ "\n"
>     let option      = key /[A-Z]+/
>     let value       = sep . ws . store /[[:alnum:]]/ . ws
>     let values      = [ seq "value" . value ] +
>     let setting     = [ br_l . option . values . br_r ]
>     let record      = setting . comment
>     let lns         = ( record | comment ) . eol
>     (*
>     let lns         = ( setting?. comment . eol )
>     *)
>
> I posted an ambiguous grammar first because it is easier to comprehend -
> always use the leftmost rule/union of lns to generate the tree and
> backtrack if necessary. The following is an unambiguous grammar of the same
> language which is useless to Augeas:
>
>     let lns     = del ( /[[]/ "[" ) . P1 | del ( /[^[]/ ) .  NP
>     let P1      = key ( /[A-Z]+/ ) . P2 | del ( /[^A-Z]/ ) . NP
>     let P2      = del ( /[:]/ ":" ) . P3 | del ( /[^:]/ "" ) . NP
>     let P3      = del ( /[ \t]*/ "" ) . P4
>     let P4      = store /[[:alnum:]]+/ . P5 | del ( /[^[:alnum:]]/ "" ) .
> NP
>     let P5      = del ( /[ \t]*/ "" ) . P2
>     let NP      = del ( /[^\n]*/ . /\n/ ) ""
>
> The shortcoming is the second rule of P2. While a valid tree, as a parser
> it is unable to differentiate and recall a valid closing brace from junk.
> The following grammar solves this:
>
>
>     let lns     = del ( /[[]/ "[" ) . P1 | del ( /[^[]/ ) .  NP
>     let P1      = key ( /[A-Z]+/ ) . P2 | del ( /[^A-Z]/ ) . NP
>     let P2      = del ( /[:]/ ":" ) . P3 | del ( /[^:]/ "" ) . NP
>     let P3      = del ( /[ \t]*/ "" ) . P4
>     let P4      = store /[[:alnum:]]+/ . P5 | del ( /[^[:alnum:]]/ "" ) .
> NP
>     let P5      = del ( /[ \t]*/ "" ) . P6
>     let P6      = del ( /[:]/ ":" ) . P3 | del ( /[]]/ "]" END | [^]:] NP
>     let END      = [^\n]* \n
>     let P7      = <big problem> END
>
>
> Since the previous two grammars no longer backtrack, augeas will generate
> invalid key/value nodes, remembered values, and subtrees. The idea is to
> have these deleted in P7, which is clearly not possible. Furthermore since
> the language implemented by Augeas is relatively pure, it isn't possible to
> imperatively set flags in rules P1-P6 and generate all the necessary keys,
> values and subtrees in END. I've also experimented with the regex_match and
> lens_ctype builtin functions, and the regex subtraction operator (which is
> unintuitive) to no avail.
>
> In other words, there is no meaningful or worthwhile expression of this
> configuration syntax in Augeas schema - at least not without repeating the
> patterns/regexes at least three(!) times, which is a maintainer's nightmare.
>
> However, the operators proposed in [2] ("||", "..", "**") and my addition,
> "??" would nicely solve this dilemma.
>
> Sincerely,
>
>
>
>
> [1] "
> Change this to turn sound off.
>
> [SOUND:YES]
> [FONT:curses_640x300.png]
> [RESIZABLE:YES]You may disable window resizing if you wish.
>
> [PRINT_MODE:2D]
>     Mode examples:
> [SINGLE_BUFFER:NO]
> [EMBARK_RECTANGLE:4:4]
>
> Change these numbers to set the default weights for traffic designations.
> If you make the last numbers too large, pathfinding might lag.
> The format is (PATH_COST:<high>:<normal>:<low>:<restricted>).
> [PATH_COST:1:2:5:25]
> "
>
> [2]
> http://www.redhat.com/archives/augeas-devel/2010-September/msg00027.html
>
> _______________________________________________
> augeas-devel mailing list
> augeas-devel at redhat.com
> https://www.redhat.com/mailman/listinfo/augeas-devel
>

-- 
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