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problem with active patterns with F# 1.9.6.2
f#

Hello.

The following code is work well in 1.9.[234].* but hangs with error under F# 1.9.6.2:
Microsoft.FSharp.Core.MatchFailureException: Exception of type 'Microsoft.FSharp.Core.MatchFailureException' was thrown.
at FSI_0002.f@4.Invoke(XmlNode n)
at Microsoft.FSharp.Collections.Seq.takeOuter@665@665[A,B](ConcatEnumerator`2 x@665, Unit _unit)
at Microsoft.FSharp.Collections.Seq.ConcatEnumerator`2.System-Collections-IEnumerator-MoveNext()
at Microsoft.FSharp.Collections.Seq.to_list[A](IEnumerable`1 ie)
at FSI_0002.parse(XmlNode inp)
at <StartupCode$FSI_0002>.$FSI_0002._main()

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#light

open System.Xml

let Select (|P|_|) (x: #XmlNode) = [ for P y as n in x.ChildNodes -> y ]

let (|Elem|_|) name (inp: #XmlNode) = 
    if inp.Name = name then Some(inp) 
    else None

let (|Attr|_|) attr (inp: #XmlNode) = 
    match inp.Attributes.GetNamedItem(attr) with
    | null -> None
    | node -> Some(node.Value)

let (|Num|_|) attr inp = 
    match inp with 
    | Attr attr v -> Some v // (Integer.of_string v) 
    | _           -> None

let (|Str|_|) attr inp = 
    match inp with 
    | Attr attr v -> Some v 
    | _           -> None

type scene = 
    | Packet of string * string * string
    | Link of string * string * string * string
    | LinkAttr of string * string * string * string * string
    | Object of string * string * string * string
    | Document of string * string * string * string
    | ObjectAttr of string * string * string

let rec (|ShapeElem|_|) inp = 
    match inp with 
    | Elem "ChangePacket" (Num "ID" id & Num "PartyID" pId & Num "SourcePartyID" spId) -> Some (Packet (id,pId,spId)) 
    | Elem "AddLink" (Num "ID" id & Num "ParentID" pId  & Num "ChildID" cId & Str "ChangeDescription" d) -> Some (Link (id,pId,cId,d))
    | Elem "UpdateLinkAttr" (Num "ID" id & Num "ParentID" pId & Num "ChildID" cId & Num "TypeID" tId & Str "ChangeDescription" d) -> Some (LinkAttr (id,pId,cId,tId,d))
    | Elem "AddObject" (Num "ID" id & Num "ObjectID" oId & Num "TypeID" tId & Str "Name" name) -> Some (Object (id,oId,tId,name)) 
    | Elem "UpdateObjectAttr" (Num "ID" id & Num "ObjectID" oId & Num "TypeID" tId) -> Some (ObjectAttr (id,oId,tId))
    | Elem "AddDocument" (Num "ID" id & Num "ObjectID" oId & Num "DocTypeID" tId & Str "OriginalFilePath" path) -> Some (Document (id,oId,tId,path)) 
    | _ -> None

and (|ShapeElems|) inp = Select (|ShapeElem|_|) inp 


let parse inp = 
    match (inp :> XmlNode) with 
    | Elem "root" (ShapeElems elems) -> elems
    | _                               -> failwith "not a scene graph"

let doc = new XmlDocument()

do doc.Load "c:/ssp/pzmash/1.xml"
let l = parse doc.DocumentElement

I'm test same correct xml file and only under F# 1.9.6.2 programs hungs in Select function on first attempt to convert root's ChildNodes to list.

.

"for P x in ..." is an incomplete pattern. You will have got a deprecation warning for this prior to 1.9.6, saying that the feature is deprecated and incomplete patterns will give exceptions when used in for loops.

This deprecated feature was removed in 1.9.6, and you do now get the MatchFailureException.

This feature was removed to make "for P x in ..." consistent and symmetric for all the places this occurs in the language. Having it silently skip elements for sequence expressions alone made some code samples cuter but was too subtle.

Thanks

Don

By on 9/29/2008 8:00 AM ()

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