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Error 6 Type mismatch. Expecting a  'foo Foo but given a  'a Foo. The type ''foo' does not match the type ''a'. C:\Documents and Settings\Cameron\My Documents\Visual Studio 2008\Projects\Epoch\EpochSimulation\rules.fs 17 12 

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type 'a Foo(pos:int*int) =
	let mutable pos = pos
	member s.Position (*Compile error here*)
		with get() = pos
		and set(v) = pos <- v
and 'foo Bar when 'foo :> 'foo Foo (src, dest) =
	let src : 'foo = src
	let dest : 'foo = dest
	member s.Test = src.Position

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type 'a Foo(pos:int*int) =
   let mutable pos = pos
   member s.Position
      with get() = pos
      and set(v) = pos <- v
and 'foo Bar when 'foo :> 'foo Foo (src, dest) =
   let src : 'foo = src
   let dest : 'foo = dest
   member s.Src = src

//member s.Test = src.Position
type 'foo Bar with
   member s.Test = s.Src.Position

However, this seems to crash the interactive window with:

type 'a Foo = class
   end
   with
      member Position : int * int with set
      member Position : int * int
      new : pos:(int * int) -> 'a Foo
   end
and Bar<'foo when 'foo :> 'foo Foo> = class
   end
   with
      member Test : int * int
      member Src : 'foo
      new : src:'foo * dest:'foo -> 'foo Bar
   end

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FS0193: System.TypeLoadException: Could not load type 'Foo`1' from assembly 'FSI-ASSEMBLY, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'.
at System.Reflection.Emit.TypeBuilder._TermCreateClass(Int32 handle, Module module)
at System.Reflection.Emit.TypeBuilder.CreateTypeNoLock()
at System.Reflection.Emit.TypeBuilder.CreateType()
at Microsoft.Research.AbstractIL.RuntimeWriter.traverseTypeRef@1696.Invoke(Int32 priority, TypeRef tref)
at Microsoft.Research.AbstractIL.RuntimeWriter.createTypeRef(HashMultiMap`2 visited, HashMultiMap`2 created, emEnv emEnv, TypeRef tref)
at Microsoft.Research.AbstractIL.RuntimeWriter.buildTypeDefPass4(HashMultiMap`2 visited_0, HashMultiMap`2 visited_1, List`1 nesting, emEnv emEnv, TypeDef tdef)
at Microsoft.Research.AbstractIL.RuntimeWriter.buildTypeDefPass4@1717.Invoke(TypeDef tdef@1710)
at Microsoft.FSharp.Collections.PrivateListHelpers.iter[T](FastFunc`2 f, List`1 x)
at Microsoft.Research.AbstractIL.RuntimeWriter.buildModuleFragment@1748.Invoke(TypeDef tdef@1731)
at Microsoft.FSharp.Collections.PrivateListHelpers.iter[T](FastFunc`2 f, List`1 x)
at Microsoft.Research.AbstractIL.RuntimeWriter.buildModuleFragment(cenv cenv, emEnv emEnv, AssemblyBuilder asmB, ModuleBuilder modB, ModuleDef m)
at Microsoft.Research.AbstractIL.RuntimeWriter.emitModuleFragment(MscorlibRefs ilg, emEnv emEnv, AssemblyBuilder asmB, ModuleBuilder modB, ModuleDef modul)
at Microsoft.FSharp.Compiler.Interactive.Shell.processInputs[T](T i, InteractionState istate, List`1 inputs, Boolean showTypes, Boolean isIncrementalFragment, List`1 prefixPath)
at Microsoft.FSharp.Compiler.Interactive.Shell.evalDefns(InteractionState istate, Boolean showTypes, List`1 defs)
at Microsoft.FSharp.Compiler.Interactive.Shell.mainThreadProcessParsedInteraction(Boolean exitViaKillThread, FastFunc`2 processInteractiveFile, Option`1 action, InteractionState istate)