Re: StringCvt.cs with regex matching

Great.  Thanks for such a detailed response.

On Tue, Oct 18, 2016 at 9:19 AM, Matthew Fluet <[email protected]>
wrote:

> On Sun, Oct 16, 2016 at 6:54 PM, Thomas Logan <[email protected]>
> wrote:
> > I'm using StringCvt.scanString for regex matching, which requires a
> > StringCvt.cs, and thus the match_tree is required to use StringCvt.cs.
> The
> > type checker won't allow using StringCvt.cs as an int.  Is there a way to
> > convert it to an int?
> >
> > Error: ...
> >   Case object and rules disagree.
> >     object type:  (_ * {pos: [StringCvt.cs], ...} MatchTree.match_tree)
> option
> >     rules expect: (_ * {pos: [int], ...} MatchTree.match_tree) option
>
> It looks like you are using the SML/NJ RegExp library:
>   http://www.smlnj.org/doc/smlnj-lib/Manual/regexp-lib-part.html#section:0
>
> The Basis Library specification states that the StringCvt.cs type is
> opaque, so there isn't a conversion from StringCvt.cs to int (in MLton;
> SML/NJ seems to expose the implementation of StringCvt.cs as int).
>
> You can write your own "scanString" function that reveals the state type
> as int:
>
>
> structure RE = RegExpFn(structure P = AwkSyntax
>                         structure E = BackTrackEngine)
> structure MatchTree =
> struct
>   open MatchTree
>   fun toString s (Match (x, mts)) : string =
>      concat ["Match (", s x, ", ",
>              "[", String.concatWith "," (List.map (toString s) mts), "]",
>              ")"]
> end
>
> fun scanString f s =
>    let
>       fun strRdr i =
>          if i >= String.size s
>             then NONE
>             else SOME (String.sub (s, i), i + 1)
>    in
>       case f strRdr 0 of
>          NONE => NONE
>        | SOME (x, _) => SOME x
>    end
>
> val re = RE.compileString "l(mn)o"
> val s = "abcdefghijklmnopqrstuvwxyz"
>
> val _ =
>    case scanString (RE.find re) s of
>       NONE => print "no match\n"
>     | SOME mt => print (concat ["Match: ",
>                                 MatchTree.toString
>                                 (fn {len, pos} => concat ["{len = ",
> Int.toString len,
>                                                           ",pos = ",
> Int.toString pos, "}"])
>                                 mt,
>                                 "\n"])
>
> [mtf@uller tmp]$ mlton z.mlb
>
> [mtf@uller tmp]$ ./z
>
> Match: Match ({len = 4,pos = 11}, [Match ({len = 2,pos = 12}, [])])
>
> --
> You received this message because you are subscribed to the Google Groups
> "MLton-user" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to [email protected].
>
> ------------------------------------------------------------
> ------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, SlashDot.org! http://sdm.link/slashdot
> _______________________________________________
> MLton-user mailing list
> [email protected]; [email protected]
> https://lists.sourceforge.net/lists/listinfo/mlton-user
>
>

-- 
You received this message because you are subscribed to the Google Groups "MLton-user" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most 
engaging tech sites, SlashDot.org! http://sdm.link/slashdot

_______________________________________________
MLton-user mailing list
[email protected]; [email protected]
https://lists.sourceforge.net/lists/listinfo/mlton-user