Mauricio Scheffer mausch

Intend to support all selectors and operators listed here in one form or another.

let (?) (doc : BsonDocument) (field : string) =
    unbox doc.[field]

let (?<-) (doc : BsonDocument) (field : string) value =
    doc.[field] = unbox value |> ignore

The Indexed Privilege Monad in Haskell, Scala, and C#

We've already looked at two different indexed monads in our tour so far, so let's go for a third whose regular counterpart isn't as well known: the privilege monad.

Motivation

The regular privilege monad allows you to express constraints on which operations a given component is allowed to perform. This lets the developers of seperate interacting components be statically assured that other components can't access their private state, and it gives you a compile-time guarantee that any code that doesn't have appropriate permissions cannot do things that would require those permissions. Unfortunately, you cannot easily, and sometimes cannot at all, build code in the privilege monad that gains or loses permissions as the code runs; in other words, you cannot (in general) raise or lower your own privilege level, not even when it really should be a

	private xxx func1(args, ..., GLOBAL) { ... func2(..., GLOBAL) ... }
	private xxx func2(args, ..., GLOBAL) { ... func3(..., GLOBAL) ... }
	private xxx func3(args, ..., GLOBAL) { ... func1(..., GLOBAL) ... }

	public xxx func(args, ..., global) { ... func1(..., global) ... }

	// "GLOBAL" representa un estado de entrada que no forma parte de
	// la clase (de hecho la clase podría ser estática), porque lo que
	// interesa es el proceso que realizan las funcX.

	Feature: The Data.List module

	In order to be able to use lists
	As a programmer
	I want a module that defines list functions

	Scenario: Defining the function foldl
	Given I want do define foldl
	Which has the type (in brackets) a to b to a (end of brackets), to a, to list of b, to a
	And my arguments are called f, acc, and l

	id,_version_,BRAND_s,_root_,type_s,COLOR_s,SIZE_s
	12,,,10,,Blue,XL
	11,,,10,,Red,XL
	10,1445176108735528960,Nike,10,parent,,
	22,,,20,,Blue,XL
	21,,,20,,Red,M
	20,1445176108738674688,Nike,20,parent,,
	32,,,30,,Blue,M
	31,,,30,,Red,XL
	30,1445176108740771840,Puma,30,parent,,

	// http://homepages.inf.ed.ac.uk/slindley/papers/handlers-draft-march2013.pdf
	// Quote from the paper
	// Effect handler operation clauses generalise exception handler clauses
	// by adding a continuation argument, providing support for arbitrary effects. An operation
	// clause is an exception clause if it ignores its continuation argument.

	type Cont<'T, 'R> = Cont of ((('T -> 'R) * (exn -> 'R)) -> 'R)

	type ContBuilder() =
	member self.Return x = Cont (fun (k, _) -> k x)

	module Partiality where

	import Control.Monad.Free

	type Partiality = Free Maybe

	never :: Partiality a
	never = Free $ Just never

	bad :: Partiality a

	Following http://stackoverflow.com/questions/11123777/how-to-generate-c-friendly-net-4-0-compatible-types-using-f-3-0-type-provide I was able to compile the project using csc.exe directly by including the missing reference to fsharpx (see the full call below) and placing the dlls such that the generated .exe could find them. And the result was
	[1; 2; 3]
	Some(5)

	The abovementioned url suggest that the problem can be solved by specifying SpecificVersion=true for the reference to FSharp.Core 4.3 (in FSharpx.Core.fsproj). I tried to do this and compiled FSharpx.Core (I had to add System.Numerics to the project though), and it seems to solve the problem. It is a bit unfortunate to be dependent on a particular version, but it seems to be the only solution at the moment.

	The full call to csc.exe (on my machine)
	C:\Windows\Microsoft.NET\Framework\v4.0.30319\Csc.exe /noconfig /nowarn:1701 /nostdlib+ /platform:x86 /errorreport:prompt /warn:4 /define:DEBUG /reference:"C:\Program Files (x86)\Reference Assemblies\Micro

	This was my approach

	Downloading the dependencies via nuget, but the dependency on 'FSharp.Core' reference is marked with an error and I get the following errors and warnings if I try to compile (the first 2 are the essential ones):

	Warning 1 The primary reference "FSharp.Core, Version=4.3.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has a higher version "4.3.0.0" than exists in the current target framework. The version found in the current target framework is "4.0.0.0". FSharpxCSharp
	Warning 2 The primary reference "FSharpx.Core" could not be resolved because it has an indirect dependency on the .NET Framework assembly "FSharp.Core, Version=4.3.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which has a higher version "4.3.0.0" than the version "4.0.0.0" in the current target framework. FSharpxCSharp
	Warning 3 The referenced component 'FSharp.Core' could not be found.
	Error 4 The type or namespace name 'FSharpx' could not be f