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bug? - gaurded pattern match changing immutable variable value
f#.net

(*

F# - F sharp

Note orginal progrm was much larger i made it very small to remove as much confusion as possible

The problem is in a guarded pattern match - when a int variable is checked against another int variable for greater than or equal. The immutable variable value on the right side or the variable being checked against is being changed to the vaule of the varaible it is being compared agains. Additionally, the subsiquent function and or line of code that should be executed is not.

my environment:

Microsoft Visual Studio 2010

Version 10.0.20506.1 Beta1

Microsoft .NET Framework

Version 4.0

Installed Version: Professional

Microsoft Silverlight Projects 2010 91605-005-5610054-60629

Microsoft Silverlight Projects 2010

Version 10.0.20506.1

Microsoft Visual Basic 2010 91605-005-5610054-60629

Microsoft Visual Basic 2010

Microsoft Visual C# 2010 91605-005-5610054-60629

Microsoft Visual C# 2010

Microsoft Visual C++ 2010 91605-005-5610054-60629

Microsoft Visual C++ 2010

Microsoft Visual F# 2010 91605-005-5610054-60629

Microsoft Visual F# 2010

Microsoft Visual Studio 2010 Tools for the Microsoft Office system 91605-005-5610054-60629

Microsoft Visual Studio 2010 Tools for the Microsoft Office system

Microsoft Visual Web Developer 2010 91605-005-5610054-60629

Microsoft Visual Web Developer 2010

Workflow Designer Package 1.0

Package for WPF based Microsoft Workflow Designer

i think code says it all - i have enclodes the code i have not read how to post code so spacing looks wrong

*)

#light

open System

let baseloop = ref 0

let actionlength = 3

let input = 4

match input with

| actionlength when input > actionlength -> baseloop := !baseloop + 99 //this never happends

| mlist when input (*less than symbol *) actionlength -> System.Diagnostics.Process.Start("notepad") //there always has to be a line with a command after this .net object - interactive does not like this line but it compiles and run it is not the main problem

Console.Clear()

| _ -> Console.Clear()

printf "%A %i" baseloop actionlength //baseloop is still 0 not correct and actionlength is 4

printf "press enter"

System.Console.ReadKey(true)

.

you can use ``ignore'' to get rid of the warnings:

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System.Diagnostics.Process.Start("notepad") |> ignore

I think the problem is that the ``this never happends'' line is creating an internal var actionlength. I'm not exactly sure what the intent is here. But, try something like this:

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match input with 

    | x when x > actionlength -> baseloop := !baseloop + 99 //this should get called now

    | mlist when mlist < actionlength ->

        System.Diagnostics.Process.Start("notepad") |> ignore

        Console.Clear() 

    | _ -> Console.Clear()

Try looking at the ``local variables'' window as you step through the debugger, and you'll see that 2 actionlength variables exist inside the match statement.

By on 7/8/2009 1:59 PM ()

yes i see that now two variables with one name and different values in each.

this also works:

match input with

| _ when input > actionlength -> printf "th"

| _ when input %lt actionlength -> printf "thi"

By on 7/8/2009 2:09 PM ()

It is also possible to use a simple if-else, if you aren't matching:

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if input > actionlength then printf "th"

elif input < actionlength then printf "thi"
By on 7/9/2009 7:12 AM ()

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